Optical scanning apparatus, illuminant apparatus and image forming apparatus

ABSTRACT

An optical scanning apparatus scans a surface to be scanned in a main scanning direction by simultaneously using a plurality of optical spots formed of a plurality of optical beams emitted from an illuminant, comprising: a light path deflecting part deflecting a light path of at least one of the optical beams, wherein the light path deflecting part is provided in light paths of the optical beams wherein the light path deflecting part may use a liquid crystal deflecting element formed of a liquid crystal element being controllable by an electronic signal to deflect the light path of the one of the optical beams.

CROSS REFERENCE

This application is a division of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 10/386,654,filed Mar. 13, 2003, now U.S. Pat. No. 7,333,254 and claims the benefitof priority under 35 U.S.C. §119 from Japanese Patent Application No.2002-348581, filed Nov. 29, 2002, Japanese Patent Application No.2002-256704, filed Sep. 2, 2002, and Japanese Patent Application No.2002-072656, filed Mar. 15, 2002, the entire contents of each which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an optical scanning apparatus(multi-beam scanning apparatus) for using a plurality of optical beamsprojected from an illuminant to simultaneously scan a surface to bescanned in the main scanning direction, an illuminant apparatus preparedfor the optical scanning apparatus, and an image forming apparatus thatuses the optical scanning apparatus as an optical writing system such asa laser color printer, a digital color copier, a laser plotter and alaser facsimile.

2. Description of the Related Art

In order to improve the recording speed of an optical scanning apparatusthat is used as an optical writing system in an image forming apparatus,there is an approach in which the rotational speed of a polygon mirror,which serves as a deflecting part, is increased. However, this approachhas limited improvement with respect to the recording speed if motordurability, motor noise, motor vibration, laser modulation speed and thelike are taken into account. Consequently, optical scanning apparatusesfor simultaneously radiating a plurality of optical beams in order torecord a plurality of lines have been proposed.

Some multi-beam illuminant apparatuses that can radiate a plurality oflaser beams as an illuminant part of these optical scanning apparatuseshave been also proposed. As such a multi-beam illuminant apparatus,there is a multi-beam semiconductor laser (for instance, a semiconductorlaser array) that contains a plurality of illuminant points (illuminantchannels). Regarding such a semiconductor laser array, however, it isextremely difficult to increase the number of the illuminant channels incourse of fabrication thereof. In addition, it is hard to eliminateinfluences on thermal/electronic crosstalk and realize a shortwavelength with respect to the semiconductor laser array. For thesereasons, the semiconductor array is currently considered to be expensiveas an illuminant part of an optical scanning apparatus.

On the other hand, a single-beam semiconductor laser is widely used invarious industries because the wavelength of the single-beamsemiconductor laser can be easily shortened and the fabrication costthereof is affordable even in the current technology level.

An illuminant apparatus and a multi-beam scanning apparatus use such asingle-beam semiconductor laser or the above-mentioned multi-beamsemiconductor laser as an illuminant. In this case, the illuminantapparatus and the optical scanning apparatus need to have a beamsynthesizing part for synthesizing a plurality of laser beams. With thisbackground, a large number of illuminant apparatuses and opticalscanning apparatuses for using a beam synthesizing part to synthesize aplurality of laser beams have been proposed.

However, when such a beam synthesizing part is used to synthesize aplurality of laser beams, a single-beam semiconductor laser has someproblems in comparison with a semiconductor laser array in thatenvironmental variations and time passage make alignment of beam spotson a surface to be scanned, for instance, the beam pitch and thescanning line interval, unstable.

Japanese Laid-Open Patent Application No. 2000-227563 discloses amulti-beam scanning optical device for using a beam synthesizing prismto synthesize optical beams emitted from a plurality of illuminants. Inthis multi-beam scanning optical device, projection directions of theoptical beams are adjusted by shifting the beam synthesizing prism alonga light path and adjusting gradient of the beam synthesizing prism inthe main scanning section or the subscanning section. As a result, it ispossible to adjust positions of beam spots on a surface to be scanned.

Japanese Laid-Open Patent Application No. 10-215351 discloses a lightbeam scanner for using a beam synthesizing prism to synthesize opticalbeams emitted from a plurality of illuminants. In this light beamscanner, projection directions of the optical beams are adjusted byshifting a cylindrical lens for forming a line image on a reflectionsurface of a polygon mirror in the subscanning direction. As a result,it is possible to adjust positions of beam spots on a surface to bescanned.

Japanese Laid-Open Patent Application No. 09-189873 discloses a devicefor scanning multi-beam for using a half mirror to synthesize opticalbeams emitted from a plurality of illuminants. In this device forscanning multi-beam, projection directions of the optical beams areadjusted by adjusting gradients of a galvanomirror in a light path andan illuminant apparatus. As a result, it is possible to adjust positionsof beam spots on a surface to be scanned.

Japanese Laid-Open Patent Application No. 10-282531 discloses an opticaldeflector for deflecting a beam laser through varying refractive indexof an electrooptic material (lithium niobate and so on) withelectrooptic effect.

Japanese Laid-Open Patent Application No. 2000-003110 discloses an imageforming device and control method thereof. In this image forming device,a light path deflecting element (a liquid crystal element) is used toadjust a scanning position on a surface to be scanned, and the pitchirregularity of scanning lines, which is caused by the rotationalirregularity of a photoreceptor drum, is corrected. In addition, theimage forming device has a detecting part for detecting the rotationalspeed of the photoreceptor drum.

Japanese Laid-Open Patent Application No. 2000-047214 discloses anoptical path variable device and an image forming device. A light pathdeflecting element formed of a plurality of liquid crystal layers isprovided to an image forming apparatus for forming an image. Like theimage forming device according to Japanese Laid-Open Patent ApplicationNo. 2000-003110, the optical path variable device and the image formingdevice intends to correct the pitch irregularity of scanning linescaused by the rotational irregularity of a photoreceptor drum.

Many of existing inventions including the multi-beam scanning opticaldevice according to Japanese Laid-Open Patent application No.2000-227563, the light beam scanner according to Japanese Laid-OpenPatent application No. 10-215351, and the device for scanning multi-beamaccording to Japanese Laid-Open Patent application No. 09-189873 usesome mechanical systems to deflect a light path of an optical beam andadjust alignment of a beam spot on a surface to be scanned.

In the case where such a mechanical system is used to adjust the lightpath, however, since the number of parts thereof inevitably increases,the part increase not only undermines reliability and duration of thewhole system but also increases the system size. In addition, there is aprobability that hysteresis caused by backlash and others, vibration,noise and heat arise.

Also, some methods are presented along another approach. One methodutilizes variations of the prism refractive index caused byelectrooptical effect such as the optical deflector according toJapanese Laid-Open Patent application No. 10-282531. Also, in anothermethod, an optical beam is deflected through diffraction caused by anacoustooptic element. However, since a high driving voltage is requiredto implement these methods, an apparatus thereof becomes complicated andincludes risk of heat generation. Thus, these methods are considered tobe impractical.

In the image forming device according to Japanese Laid-Open Patentapplication No. 2000-003110 and the optical path variable device andimage forming device according to Japanese Laid-Open Patent applicationNo. 2000-047214, such an image forming apparatus uses a liquid crystalelement as a light path deflecting element so as to correct the pitchirregularity of scanning lines due to the rotational irregularity of aphotoreceptor drum or more accurately superpose image informationbetween photoreceptor drums in a tandem type optical scanning apparatus.

In a tandem type full color image forming apparatus, four photoreceptordrums corresponding to the four colors: cyan (C), magenta (M), yellow(Y) and black (K) are provided in a tandem form along the carriersurface of an intermediate transferring belt. When a beam scanningapparatus scans an image by using optical beams corresponding to theindividual photoreceptors, electrostatic latent images are formed on thecircumferential surfaces of the photoreceptor drums. The electrostaticlatent images are developed by using the corresponding color toners. Thecolor toner images are carried by the intermediate transferring belt,and then a color image is created by sequentially transferring the colortoner images.

In the beam scanning apparatus, a scanning part is rotationally drivenat a predetermined rotational speed by a polygon motor and so on. A linesynchronization signal generating part detects an optical beam from thebeam scanning apparatus at a predetermined position and then generates aline synchronization signal. Synchronously with the line synchronizationsignal, an optical beam is modulated in accordance with the imagesignal, and then the image is written for each line. An intermediatetransfer reference signal generating part detects a mark on anintermediate transfer body at a predetermined position and thengenerates an intermediate transfer reference signal. Synchronously withthe intermediate transfer reference signal, toner images correspondingto the individual colors are formed on the photoreceptor.

However, the intermediate transfer reference signal and the linesynchronization signal are not synchronized with each other in the colorimage forming apparatus. Thus, as the number of optical beams increases,the phase difference between the intermediate transfer reference signaland the line synchronization signal tends to become larger. When thedifference between the image writing start positions becomes large withrespect to the subscanning direction, there arises color smear(misalignment of the individual toner images) and the resulting colorimage deteriorates.

Japanese Laid-Open Patent Application No. 10-239939 discloses a colorimage forming device that can eliminate the above-mentioned problems.The color image forming apparatus has a correcting part correcting acolor smear by selecting the first optical beam for writing an image ona photoreceptor among a plurality of optical beams in accordance withphase relation between an intermediate transfer reference signal and aline synchronization signal and adjusting image writing start positionsof individual colors with respect to the subscanning direction. However,even if this method is applied to color image forming apparatuses, therestill is a probability that at most one line of misalignment arises withrespect to the image writing start positions.

When a liquid crystal element is used to deflect a light path by aninfinitesimal angle, it is necessary to coincide (parallel) an opticalaxis of the liquid crystal element with a plane of polarization of anoptical beam having linear polarization. In order to enhance shadingcharacteristic (light intensity distribution) on a surface to be scannedof a photoreceptor, a semiconductor laser (single beam) is inclined inthe optical axis direction. Also, in order to set a subscanning beampitch on a surface to be scanned to a predetermined value in amulti-beam scanning apparatus using a semiconductor laser array as anilluminant part thereof, the semiconductor laser array is inclined inthe optical axis direction in accordance with the optical magnification.In these cases, there is a probability that the deflection direction ofthe light path does not always coincide with the polarization plane ofthe optical beam. If the deflection direction of the light path does notcoincide with the polarization plane of the optical beam, it isimpossible to effectively deflect the light path by means of the liquidcrystal element.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an opticalscanning apparatus, an illuminant apparatus and an image formingapparatus in which the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide an opticalscanning apparatus for scanning a surface to be scanned in the mainscanning direction by simultaneously using a plurality of optical beamsemitted from an illuminant wherein the optical scanning apparatus cancorrect misalignment of the beam pitch of beam spots on the scannedsurface caused by environmental variations and time passage.

Another more specific object of the present invention is to provide asmall size illuminant apparatus that is installed suitably to theoptical scanning apparatus capable of adjusting alignment of beam spotson a surface to be scanned.

Another more specific object of the present invention is to provide animage forming apparatus that can produce a high quality output image byusing the above-mentioned optical scanning apparatus therein.

Another more specific object of the present invention is to provide anoptical scanning apparatus using a liquid crystal element wherein theoptical scanning apparatus can move a beam spot position on a surface tobe scanned by using the liquid crystal element if the direction of anactive layer of a semiconductor laser chip (the polarization plane ofthe optical beam) serving as an illuminant does not coincide with theoptical axis direction of the liquid crystal element.

Another more specific object of the present invention is to provide animage forming apparatus that installs the above-mentioned opticalscanning apparatus.

In order to achieve the above-mentioned objects, there is providedaccording to one aspect of the present invention an optical scanningapparatus for scanning a surface to be scanned in a main scanningdirection by simultaneously using a plurality of optical spots formed ofa plurality of optical beams emitted from an illuminant, comprising: alight path deflecting part deflecting a light path of at least one ofthe optical beams, wherein the light path deflecting part is provided inlight paths of the optical beams.

According to the above-mentioned invention, since the light pathdeflecting part deflects a light path of at least one of optical beams,it is possible to adjust a position of a beam spot on the scannedsurface.

In the above-mentioned optical scanning apparatus, the light pathdeflecting part may use a liquid crystal deflecting element formed of aliquid crystal element being controllable by an electronic signal todeflect the light path of the one of the optical beams.

According to the above-mentioned invention, it is possible to not onlyavoid the size increase of the optical scanning apparatus but alsosuppress vibration, noise and heat. In addition, it is possible toadjust beam spot alignment on the scanned surface by a low voltage.

In the above-mentioned optical scanning apparatus, the liquid crystaldeflecting element may be capable of deflecting optical beams separatelyin two directions orthogonal to each other.

According to the above-mentioned invention, since the optical beams canbe separately deflected toward two directions orthogonal with eachother, it is possible to adjust positions of the beam spots separatelywith respect to the main scanning direction and the subscanningdirection.

In the above-mentioned optical scanning apparatus, the liquid crystaldeflecting element may have a plurality of effective areas each of whichis separately modulated.

According to the above-mentioned invention, since each element has aplurality of effective areas, it is possible to reduce the number ofparts and improve the positioning accuracy.

In the above-mentioned optical scanning apparatus, the illuminant maycomprise at least a semiconductor laser serving as an illuminant pointand a coupling lens coupling laser light emitted from the semiconductorlaser.

According to the above-mentioned invention, when the illuminant isformed of at least a semiconductor laser and a coupling lenscorresponding to the semiconductor laser, it is possible to easilyadjust beam characteristics of an emitted optical beam such as collimateproperty and the optical axis direction in accordance with an opticalsystem in the lower stream.

In the above-mentioned optical scanning apparatus, the above-mentionedoptical scanning apparatus may further comprise a beam synthesizing partsynthesizing optical beams emitted from a plurality of illuminants.

According to the above-mentioned invention, since a plurality of opticalbeams are emitted from a plurality of distinct illuminants, it ispossible to flexibly position the illuminants and decrease a cross angleθ between two of the optical beams around a deflecting reflectionsurface of the deflector with respect to the main scanning direction.

In the above-mentioned optical scanning apparatus, each of theilluminants may comprise at least a semiconductor laser serving as anilluminant point and a coupling lens coupling laser light emitted fromthe semiconductor laser, and the semiconductor and the coupling lens maybe arranged so as to correct a synthesis error by the beam synthesizingpart.

According to the above-mentioned invention, since the relative positionof the semiconductor laser to the coupling lens is adjusted, that is,the optical axis and collimate is adjusted, in accordance with synthesiserrors, it is possible to efficiently correct the synthesis errors.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise an aperture member having an aperture forshaping an optical beam wherein the aperture member is provided in anupper stream side, that is, in an illuminant side, of the liquid crystaldeflecting element in the light paths of the optical beams.

According to the above-mentioned invention, since the aperture isprovided in the upper stream side of the liquid crystal element, it ispossible to reduce the size of the effective area of the liquid crystalelement.

In the above-mentioned optical scanning apparatus, the aperture forshaping an optical beam may be formed on one of an entrance surface andan exit surface of the liquid crystal deflecting element.

According to the above-mentioned invention, since the aperture is formedon the entrance surface or the exit surface, it is possible to reducethe number of parts and improve the positioning accuracy of the apertureand the effective area of the liquid crystal element.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise a detecting part detecting positions ofthe optical spots for simultaneously scanning the surface to be scannedand a driving part driving/controlling a liquid crystal deflectingelement based on a detection result of the detecting part so as toadjust a position of at least one of the optical spots.

According to the above-mentioned invention, since positions of the beamspots are detected and are adjusted based on detection results, it ispossible to efficiently suppress deterioration of the beam spotalignment caused by temperature fluctuation and time passage.

Additionally, there is provided according to another aspect of thepresent invention an illuminant apparatus for emitting a plurality ofoptical beams and serving an optical scanning apparatus for scanning asurface to be scanned in a main scanning direction by simultaneouslyusing a plurality of optical spots formed of the optical beams emittedfrom a plurality of illuminants therein, wherein the optical scanningapparatus comprises a light path deflecting part, which is provided inlight paths of the optical beams, deflecting a light path of at leastone of the optical beams, comprising: a plurality of light pathdeflecting parts separately deflecting one of the optical beamscorresponding to each of the light path deflecting parts, wherein thelight path deflecting parts are integrally provided.

According to the above-mentioned invention, since positions of the beamspots are adjusted and a plurality of light path deflecting elements areintegrally provided, it is possible to miniaturize the illuminantapparatus.

In the above-mentioned illuminant apparatus, the light path deflectingpart may be formed of a transmission type optical element and may beprovided in light paths of the optical beams.

According to the above-mentioned invention, it is possible to adjustpositions of the beam spots with high revolving power.

In the above-mentioned illuminant apparatus, the light path deflectingpart may be formed of a reflection type optical element and may beprovided in light paths of the optical beams.

According to the above-mentioned invention, it is possible to adjustpositions of the beam spots in a wide range.

In the above-mentioned illuminant apparatus, the transmission typeoptical element may be driven by a driving part using a piezoelectricelement.

In the above-mentioned illuminant, the reflection type optical elementmay be driven by a driving part using a piezoelectric element.

According to the above-mentioned inventions, since the light pathdeflecting part is driven by a difference of the piezoelectric elementin proportion to an applied voltage, it is possible to attain a desiredadjustment value at high revolving power. Also, when a ring ultrasoundmotor is used to drive the light path deflecting element, it is possibleto attain high retention even if the power supply is OFF. As a result,it is possible to suppress fluctuation of the adjustment value caused byvibration and shock from an image forming apparatus and so on.

In the above-mentioned illuminant apparatus, the transmission typeoptical element may be driven by a driving part using one of a pulsemotor capable of rotating by a predetermined angle in accordance with aninput pulse signal and a pulse motor capable of moving straight by apredetermined distance in accordance with an input pulse signal.

In the above-mentioned illuminant apparatus, the reflection type opticalelement may be driven by a driving part using one of a pulse motorcapable of rotating by a predetermined angle in accordance with an inputpulse signal and a pulse motor capable of moving straight by apredetermined distance in accordance with an input pulse signal.

According to the above-mentioned invention, since the light pathdeflecting element is driven by the pulse motor generating a differencein proportion to the number of an input pulse, it is possible to obtaina desired adjustment value. Also, since the illuminant apparatus isformed of an ordinary pulse motor, it is possible to fabricate theilluminant apparatus at low cost.

In the above-mentioned illuminant apparatus, the light path defectingpart may be formed of a liquid crystal element driven by an electronicsignal.

According to the above-mentioned invention, it is possible to provide areliable illuminant apparatus that can reduce environmental loads. Also,the illuminant apparatus can freely deflect a plurality of laser beamshaving different wavelengths from each other.

In the above-mentioned illuminant apparatus, the illuminant apparatusmay further comprise a first illuminant part integrally having aplurality of illuminants aligned in line in the main scanning direction,a second illuminant part integrally having a plurality of illuminantsaligned in line in the main scanning direction, and a beam synthesizingpart making optical beams emitted from the first illuminant part and thesecond illuminant part close to each other and emitting the closeoptical beams.

According to the above-mentioned invention, since the illuminantapparatus is divided into the first illuminant part and the secondilluminant part and uses the beam synthesizing part to synthesizeoptical beams emitted from the first illuminant part and the secondilluminant part, it is possible to easily adjust an initial setting,flexibly position the illuminant apparatus, and provide LD control andthe driving substrate in common.

In the above-mentioned illuminant apparatus, the illuminants maycomprise a plurality of semiconductor lasers and a plurality of couplinglenses corresponding to the semiconductor lasers.

According to the above-mentioned invention, it is possible toarbitrarily and easily adjust the beam characteristics of optical beamsemitted from the illuminants.

In the above-mentioned illuminant apparatus, the illuminant apparatusmay further comprise an aperture member having an aperture for shapingan optical beam, wherein the aperture member is provided in an uppersteam side, that is, an illuminant side, of the light path deflectingparts.

According to the above-mentioned invention, it is possible to narrow theeffective areas of the light path deflecting part.

Additionally, there is provided according to another aspect of thepresent invention an optical scanning apparatus for scanning a surfaceto be scanned in a main scanning direction by simultaneously using aplurality of optical spots formed of a plurality of optical beamsemitted from a plurality of illuminants in an illuminant apparatuswherein the illuminant apparatus comprises a plurality of light pathdeflecting parts, which is integrally provided therein, deflecting oneof the optical beams corresponding to each of the light path deflectingparts, comprising: a detecting part detecting positions of the opticalspots for simultaneously scanning the surface to be scanned; and adriving part driving/controlling the light path deflecting parts basedon a detection result of the detecting part so as to adjust a positionof at least one of the optical spots.

According to the above-mentioned invention, since the positions of thebeam spots are detected and the light path deflecting part is drivenbased on detection results, it is possible to correct misalignment ofthe beam spots caused by temperature fluctuation and time passage.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise a deflector deflecting the optical beamsemitted from the illuminants and a scanning type imaging system scanningthe surface to be scanned by using the optical spots formed of theoptical beams deflected, wherein the optical beams from the illuminantsenter the deflector non-parallel with each other with respect to themain scanning section.

According to the above-mentioned invention, it is possible to properlyset the pitch of two optical beams with respect to the main scanningdirection and obtain synchronization detecting signals separately.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise an illuminant apparatus formed of aplurality of illuminants, a beam synthesizing part synthesizing aplurality of optical beams emitted from the illuminant apparatus, adeflector deflecting the optical beams synthesized by the beamsynthesizing part, and a scanning part leading the optical beamsdeflected by the deflector on the surface to be scanned, wherein thelight path deflecting part is provided between the illuminants and thebeam synthesizing part so as to adjust positions of the optical beams onthe surface to be scanned.

According to the above-mentioned invention, it is possible to adjustpositions of the beam spots on the scanned surface.

In the above-mentioned optical scanning apparatus, the light pathdeflecting part may be formed of a transmission type optical elementthat is eccentrically provided.

According to the above-mentioned invention, it is possible to adjustpositions of the beam spots with high revolving power.

In the above-mentioned optical scanning apparatus, the light pathdeflecting part may be formed of a liquid crystal element controllableby an electronic signal.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise a ghost light removing part removingghost light caused by the liquid crystal element, wherein the ghostlight removing part is provided as a slit aperture between the liquidcrystal element and the deflector.

According to the above-mentioned invention, it is possible to removeunnecessary optical beams.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise an aperture shaping an optical beam,wherein the aperture is provided in an upper stream side, that is, anilluminant side, of the light path deflecting part and the followingformula is satisfied;L>(½)×tan θ×(b+Δ),where b is a breadth of optical beams deflected by the liquid crystalelement, Δ is a breadth of the slit aperture, L is a distance betweenthe liquid crystal element and the slit aperture, and 2θ is an anglebetween +1st-order light and −1st-order light of the ghost light causedby the liquid crystal element.

According to the above-mentioned invention, it is possible toefficiently interrupt harmful ghost light.

In the above-mentioned optical scanning apparatus, the optical scanningapparatus may further comprise an optical housing accommodating partsthereof, wherein the optical housing holds the illuminant apparatus on aside wall thereof and holds the light path deflecting part and the beamsynthesizing part on a common holding part therein.

According to the above-mentioned invention, when the illuminantdeteriorates, it is possible to easily replace the illuminant and reducethe number of parts.

Additionally, there is provided according to another aspect of thepresent invention an image forming apparatus for forming an image,comprising: an optical scanning apparatus for scanning a surface to bescanned in a main scanning direction by simultaneously using a pluralityof optical spots formed of a plurality of optical beams emitted from anilluminant comprising a light path deflecting part deflecting a lightpath of at least one of the optical beams, wherein the light pathdeflecting part is provided in light paths of the optical beams; aphotoreceptor forming an electrostatic latent image scanned by theoptical scanning apparatus; a developing apparatus developing theelectrostatic latent image as a toner image with a toner; and atransferring apparatus transferring the toner image in a recordingmedium.

Additionally, there is provided according to another aspect of thepresent invention an image forming apparatus for forming an image,comprising: an optical scanning apparatus for scanning a surface to bescanned in a main scanning direction by simultaneously using a pluralityof optical spots formed of a plurality of optical beams emitted from aplurality of illuminants in an illuminant apparatus wherein theilluminant apparatus comprises a plurality of light path deflectingparts, which is integrally provided therein, deflecting one of theoptical beams corresponding to each of the light path deflecting parts,comprising a detecting part detecting positions for simultaneouslyscanning the surface to be scanned and a driving partdriving/controlling the light path deflecting parts based on a detectionresult of the detecting part so as to adjust a position of at least oneof the optical spots; a photoreceptor forming an electrostatic latentimage scanned by the optical scanning apparatus; a developing apparatusdeveloping the electrostatic latent image as a toner image with a toner;and a transferring apparatus transferring the toner image in a recordingmedium.

According to the above-mentioned inventions, since the image formingapparatus uses the optical scanning apparatus capable of scanning ascanned surface by simultaneously using a plurality of optical beams, itis possible to achieve high-speed printing and produce a high-densityimage. Also, if the speed and the density are suppressed at the samelevels as a single beam illuminant apparatus, it is possible to decreaserotation speed of a deflector such as a polygon mirror. As a result, itis possible to reduce electricity consumption, vibration, noise andheat.

In the above-mentioned image forming apparatus, the light pathdeflecting part may be driven/controlled by an operator based on anoutput image on the recording medium.

According to the above-mentioned invention, since the operator candetermine the quality of an image based on the output image on therecording medium and control the light path deflecting element, it ispossible to correct deterioration of the image including influences onthe output image by the developing process, the transferring process andthe fixing process. Also, since either or both of the beam spotalignment detecting part or/and the beam spot alignment control part maybe omitted, it is possible to fabricate the image forming apparatus withlow cost.

In the above-mentioned image forming apparatus, the image formingapparatus may further comprise a plurality of the photoreceptors servingas a plurality of surfaces to be scanned.

According to the above-mentioned invention, it is possible to produce ahigh-density monochrome or color image at high speed.

In the above-mentioned image forming apparatus, the image formingapparatus may further comprise a plurality of the optical scanningapparatuses wherein the optical scanning apparatuses are aligned in linein the main scanning direction for the photoreceptor.

According to the above-mentioned invention, it is possible to suppresscolor difference of an output image and image deterioration around aconnection area between optical beams.

In the above-mentioned image forming apparatus, the image may havevariable pixel density.

According to the above-mentioned invention, it is possible to change thepixel density by switching operation modes such as a printer mode and acopier mode in accordance with purposes of an operator.

Additionally, there is provided according to another aspect of thepresent invention an optical scanning apparatus for scanning a surfaceto be scanned by using a beam spot formed of an optical beam emittedfrom a semiconductor laser, comprising: a liquid crystal elementdeflecting a light path of the optical beam on the surface to bescanned; and a light rotating part rotating a polarization plane of theoptical beam.

According to the above-mentioned invention, it is possible toefficiently deflect a light path of an optical beam by using the liquidcrystal element and adjust positions of the beam spots.

In the above-mentioned optical scanning apparatus, the light rotatingpart may be formed of a ½ wavelength plate.

According to the above-mentioned invention, since such a small andreasonable ½ wavelength plate is used as the light rotating part, it ispossible to avoid the size increase of the optical scanning apparatusand fabricate the optical scanning apparatus as low costs.

In the above-mentioned optical scanning apparatus, the ½ wavelengthplate may be held by a rotation adjusting part and may be capable ofrotating upon an optical axis.

According to the above-mentioned invention, it is possible to coincidethe polarization plane of the laser beam with the optical axis of theliquid crystal element by rotating the polarization plane by apredetermined angle.

In the above-mentioned optical scanning apparatus, a position of theoptical spot may be adjusted on the surface to be scanned by deflectinga light path of the optical beam in a subscanning section of the liquidcrystal element.

According to the above-mentioned invention, it is possible to virtuallyadjust a position of the beam spot with respect to only the subscanningdirection. As a result, it is possible to eliminate some problems causedby misalignment of the beam spot with respect to only the subscanningdirection.

In the above-mentioned optical scanning apparatus, the semiconductorlaser may be formed of a semiconductor laser array having a plurality ofilluminant points.

According to the above-mentioned invention, it is possible to easilyform a high-density image at high speed without increasing rotationspeed of the polygon motor for rotating a polygon mirror serving as thedeflector.

In the above-mentioned optical scanning apparatus, the semiconductorlaser array may be inclined toward an optical axis of the optical beamemitted.

According to the above-mentioned invention, it is possible to obtain adesired beam pitch regardless of magnification of the optical scanningapparatus.

In the above-mentioned optical scanning apparatus, the surface to bescanned may be scanned by an optical beam synthesized from at least twooptical beams emitted from at least two semiconductor lasers by using aPBS (Polarization Beam Splitter) surface, and the liquid crystal elementmay be arranged so as to convert an optical beam emitted from the liquidcrystal element into one of an S-polarized optical beam or a P-polarizedoptical beam toward the PBS surface.

According to the above-mentioned invention, it is possible to suppressenergy loss in the beam synthesizing part.

In the above-mentioned optical scanning apparatus, the surface to bescanned may be scanned by an optical beam synthesized from at least twooptical beams emitted from at least two semiconductor lasers by using ahalf-mirror.

According to the above-mentioned invention, optical beams aresynthesized independently of the directions of the polarization planesof the optical beams. Furthermore, since it is unnecessary to providethe light rotating part such as a ½ wavelength plate between the liquidcrystal element and the beam synthesizing prism, it is possible toreduce the number of parts and fabricate the optical scanning apparatusat low costs.

Additionally, there is provided according to another aspect of thepresent invention an image forming apparatus for forming an image,comprising: an optical scanning apparatus for scanning a surface to bescanned by using an optical spot formed of an optical beam emitted froma semiconductor laser, the optical scanning apparatus comprising aliquid crystal element deflecting a light path of the optical beam onthe surface to be scanned and a light rotating part rotating apolarization plane of the optical beam; a photoreceptor forming anelectrostatic latent image scanned by the optical scanning apparatus; adeveloping part developing the electrostatic latent image as a tonerimage with a toner; and a transferring part transferring the toner imagein a recording medium.

According to the above-mentioned invention, it is possible to obtain ahigh-quality image.

In the above-mentioned image forming apparatus, the optical scanningapparatus may scan the photoreceptor by using a plurality of beam spotsformed of a plurality of optical beams and may be capable of adjusting ascanning line pitch on the photoreceptor.

According to the above-mentioned invention, since the misalignment ofthe scanning line interval is corrected, it is possible to obtain ahigh-quality image.

In the above-mentioned image forming apparatus, the optical scanningapparatus may scan the photoreceptor by using a plurality of opticalbeams and is capable of switching a pixel density of the image.

According to the above-mentioned invention, it is possible to providethe image forming apparatus that can switch the pixel density byincorporating two image forming apparatuses having different imagedensities from each other.

Additionally, there is provided according to another aspect of thepresent invention a tandem type image forming apparatus for forming animage, comprising: an optical scanning apparatus for scanning a surfaceto be scanned by using a beam spot formed of an optical beam emittedfrom a semiconductor laser, the optical scanning apparatus comprising aliquid crystal element deflecting a light path of the optical beam onthe surface to be scanned; and a light rotating part rotating apolarization plane of the optical beam; a photoreceptor forming anelectrostatic latent image scanned by the optical scanning apparatus; adeveloping part developing the electrostatic latent image as a tonerimage with a toner; and a transferring part transferring the toner imagein a recording medium, wherein a plurality of the photoreceptors areprovided, the optical scanning apparatus scans the photoreceptors with aplurality of optical beams, and misalignment of a write start positionbetween the photoreceptors is corrected.

According to the above-mentioned invention, in order to obtain ahigh-quality image in a tandem type color image forming apparatus, it ispossible to coincide write start positions among image stations.

Additionally, there is provided according to another aspect of thepresent invention a division scanning type image forming apparatus forforming an image, comprising: an optical scanning apparatus for scanninga surface to be scanned by using a beam spot formed of an optical beamemitted from a semiconductor laser, the optical scanning apparatuscomprising a liquid crystal element deflecting a light path of theoptical beam on the surface to be scanned and a light rotating partrotating a polarization plane of the optical beam; a photoreceptorforming an electrostatic latent image scanned by the optical scanningapparatus; a developing part developing the electrostatic latent imageas a toner image with a toner; and a transferring part transferring thetoner image in a recording medium, wherein a plurality of the opticalscanning apparatuses are aligned in line with respect to a main scanningdirection for each photoreceptor and misalignment of the beam spot withrespect to a main scanning direction around a connection area betweenscanning beams from the optical scanning apparatuses is corrected.

In the above-mentioned division scanning type image forming apparatus,the misalignment of the beam spot around a connection area betweenscanning beams may be corrected with respect to a subscanning direction.

According to the above-mentioned inventions, it is possible to obtain ahigh-quality image by coinciding positions of the beam spots in aconnection area between every two of the image stations.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an optical scanning apparatus accordingto the present invention;

FIG. 2 is an outline plan view with respect to a main scanning sectionand light paths of the optical scanning apparatus;

FIG. 3 is a diagram illustrating an example of alignment on a scannedsurface of beam spots generated from two optical beams;

FIG. 4 is a diagram illustrating an angle between the two optical beamsemitted from an illuminant of the optical scanning apparatus;

FIGS. 5A and 5B are diagrams illustrating the structure and thedeflecting operation of a liquid crystal deflecting element of theoptical scanning apparatus, respectively;

FIG. 6 is a perspective view of another optical scanning apparatusaccording to the present invention;

FIGS. 7A through 7C are diagrams for explaining a liquid crystaldeflecting element for deflecting a light path of an optical beam bychanging a refractive index;

FIGS. 8A through 8C are diagrams for explaining another liquid crystaldeflecting element for deflecting a light path of an optical beam bychanging a refractive index;

FIGS. 9A and 9B are diagrams for explaining further another liquidcrystal deflecting element for deflecting a light path of an opticalbeam by changing a refractive index;

FIG. 10 is a perspective view of an illuminant of the optical scanningapparatus;

FIG. 11 is a perspective view of another illuminant of the opticalscanning apparatus;

FIG. 12 is a diagram for explaining a synthesis error by a beamsynthesizing prism;

FIG. 13 is a diagram for explaining a correction method for correctingthe synthesis error by the beam synthesizing prism;

FIG. 14 is a diagram for explaining a position of an aperture member forshaping an optical beam;

FIG. 15 is a perspective view of another optical scanning apparatusaccording to the present invention;

FIG. 16 is an outline plan view with respect to a main scanning sectionof the optical scanning apparatus;

FIG. 17 is an outline sectional view of a light path deflecting elementformed of a wedge-shaped prism in the optical scanning apparatus;

FIGS. 18A through 18C are diagram for explaining another light pathdeflecting element formed of a cylindrical lens in the optical scanningapparatus;

FIGS. 19A and 19B are diagram for explaining further another light pathdeflecting element formed of a reflective optical element in the opticalscanning apparatus;

FIGS. 20A and 20B are diagram for explaining further another light pathdeflecting element formed of a liquid crystal element in the opticalscanning apparatus;

FIG. 21 is a perspective view of an illuminant apparatus according tothe present invention;

FIGS. 22A and 22B are diagram for explaining a 4-beam illuminantapparatus in which a wedge-shaped prism is used as a light pathdeflecting element;

FIGS. 23A and 23B are diagrams illustrating an optical system combinedwith the illuminant apparatus and beam spot alignment on a surface to bescanned;

FIG. 24 is a diagram for explaining an optical axis setting method forsetting the optical axis in another illuminant apparatus according tothe present invention;

FIG. 25 is a diagram for explaining an aperture member for shaping anoptical beam in the illuminant apparatus;

FIG. 26A is a perspective view of another optical scanning apparatusaccording the present invention;

FIG. 26B is a perspective view of a variation of the optical scanningapparatus;

FIG. 27 is a diagram for explaining generation of ghost light in aliquid crystal element;

FIG. 28 is a diagram for explaining deletion of ghost light by using aghost light removing part;

FIG. 29A is a perspective view of another optical scanning apparatusaccording to the present invention;

FIG. 29B is an outline sectional view of a light path deflecting part ofthe optical scanning apparatus;

FIG. 30 is an outline plan view of another optical scanning apparatusaccording to the present invention;

FIGS. 31A and 31B are diagrams illustrating an illuminant in the opticalscanning apparatus;

FIG. 32 is a diagram illustrating another illuminant in the opticalscanning apparatus;

FIGS. 33A through 33D are schematic diagram illustrating an imageforming apparatus according to the present invention;

FIG. 34 is an outline plan view of the image forming apparatus;

FIG. 35 is a sectional view of a liquid crystal element of anotheroptical scanning apparatus according to the present invention;

FIG. 36 is an enlarged plan view of an electrode pattern;

FIG. 37 is a diagram illustrating an electronic optical characteristicof nematic liquid crystal;

FIG. 38 is a diagram illustrating a phase distribution;

FIG. 39 is a perspective view of the optical scanning apparatus;

FIG. 40 is an outline front view of a rotation adjusting part of theoptical scanning apparatus;

FIG. 41 is an outline sectional view of the rotation adjusting part ofthe optical scanning apparatus;

FIG. 42 is a diagram for explaining linear polarization with a ½wavelength plate before the rotation;

FIG. 43 is a diagram for explaining linear polarization with a ½wavelength plate after the rotation;

FIG. 44 is a front view of illuminant points of a semiconductor laserarray;

FIG. 45 is an enlarged view of alignment of beam spots on a surface tobe scanned;

FIG. 46 is a perspective view of an illuminant part and an opticalsystem of another optical scanning apparatus according to the presentinvention;

FIG. 47 is a diagram for explaining beam synthesis by a beamsynthesizing prism;

FIG. 48 is a diagram for explaining oscillation directions of linearpolarization;

FIG. 49 is a diagram illustrating an outline of an optical scanningapparatus by using a beam synthesizing prism to synthesize opticalbeams;

FIG. 50 is a diagram illustrating an outline of a 4-beam scanningapparatus by using a beam synthesizing prism to synthesize opticalbeams;

FIG. 51 is a diagram illustrating an outline of an optical scanningapparatus by using a half-mirror to synthesize optical beams;

FIG. 52 is a perspective view of a tandem type color image formingapparatus; and

FIG. 53 is a diagram roughly illustrating the structure of an imageforming apparatus in which a plurality of optical scanning apparatusesare aligned in line with respect to the main scanning direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings.

A description will now be given of an optical scanning apparatusaccording to the present invention for scanning a surface to be scannedin the main scanning direction by simultaneously using a plurality ofoptical beams emitted from an illuminant wherein the optical scanningapparatus can correct misalignment of the pitch of beam spots on thesurface to be scanned caused by environmental variations and timepassage.

In the following description, X direction, Y direction and Z directionrepresent a direction along a light path (optical axis), a main scanningdirection and a subscanning direction, respectively.

Furthermore, although the main scanning direction and the subscanningdirection generally mean a direction where a beam spot scans a surfaceto be scanned and the direction orthogonal to the main scanningdirection thereof, respectively, the main scanning direction and thesubscanning direction in this embodiment mean the main scanningdirection and the subscanning direction with respect to individual spotsin a light path, respectively.

FIG. 1 is a perspective view of an optical scanning apparatus accordingto the first embodiment.

In FIG. 1, an illuminant apparatus 18 comprises at least two pairs of asemiconductor laser 11 a and a coupling lens 12 a and a semiconductorlaser 11 b and a coupling lens 12 b. However, the illuminant apparatus18 is not limited to this configuration. Also, the semiconductor lasers11 a and 11 b may be single beam semiconductor lasers each of which hasa single illuminant point or may be multi-beam semiconductor lasers(semiconductor laser arrays) each of which has a plurality of illuminantpoints.

The semiconductor lasers 11 a and 11 b emit laser light. The couplinglenses 12 a and 12 b couple the emitted laser light, and the coupledlaser light results in two resulting optical beams (laser beams) 21 aand 21 b.

The optical beams 21 a and 21 b are shaped into the linear form by acylindrical lens 13, and the linear optical beams are projected on adeflecting reflection surface of a polygon mirror 14, which serves as adeflecting system for producing optical beams that are focused on thesubscanning direction and are linearly formed with respect to the mainscanning direction. Then, the deflected linear optical beams areprojected to an optical scanning system 15. The optical scanning systemcomprises two scanning lenses 15 a and 15 b and a reflecting mirror 15 cand produces beam spots for scanning a scanned surface 16, for instance,a photoreceptor drum.

Here, an optical scanning apparatus 20 (a multi-beam scanning apparatus)scans the scanned surface 16 by using beam spots formed of a pluralityof optical beams emitted from the illuminant apparatus 18.

When the optical scanning apparatus 20 is used as an optical writingsystem of an image forming apparatus, an optical beam is modulated inaccordance with output image data. When the optical beam enters asynchronization detecting plate 19, an electronic signal(synchronization signal) is provided as the start modulation timing.

FIG. 2 shows an optical structure and a light path of the opticalscanning system according to the first embodiment with respect to a mainscanning section parallel with the optical axis and the main scanningdirection. The two optical beams 21 a and 21 b intersect by a crossangle θ in the vicinity of a deflecting reflection surface of thepolygon mirror 14. As a result, it is possible to suppress influencescaused by differences of optical characteristics such as fieldcurvatures and magnification errors between the two optical beams 21 aand 21 b.

As is shown in FIG. 3, two beam spots BS1 and BS2 formed of the twooptical beams 21 a and 21 b are provided on the scanned surface 16 in apredetermined interval (beam pitch: PY) with respect to the mainscanning direction. In accordance with the scanning line density, thetwo beam spots BS1 and BS 2 need to have a predetermined interval (beampitch: PZ) with respect to the subscanning direction. In order toprovide the beam pitch PZ, the two optical beams 21 a and 21 b areprojected at an angle φ between the outgoing directions thereof withrespect to the subscanning section.

In FIG. 1, a liquid crystal deflecting element 28 is provided as a lightpath deflecting part between the coupling lenses 12 a and 12 b and thecylindrical lens 13 in light paths of the two optical beams 21 a and 21b. The liquid crystal deflecting element 28 comprises two liquid crystalelements 28 a and 28 b. If the liquid crystal elements 28 a and 28 b aredriven/controlled (modulated) by electronic signals, it is possible toseparately deflect two optical axes of the optical beams 21 a and 21 b.As a result, it is possible to set the angle φ to a desired value.

Here, both of the optical beams 21 a and 21 b may be deflected, or oneof the optical beams 21 a and 21 b may be deflected.

Conventional light path deflecting parts deflect an optical beam basedon some methods. The first method is related to a mechanical approach.In this method, for instance, an optical beam is deflected by moving amirror or a prism in the light path thereof. The second method isrelated to an approach using an electrooptic element. In this method, anoptical beam is deflected by using material characteristics of anelectrooptic element to change the refraction index of a prism. Thethird method is related to an approach using acousto-optic element. Inthis method, for instance, an optical beam is deflected by generating adiffraction grating in a piezoelectric body through an ultrasonic wave.

However, any of these methods has some disadvantages. For instance, evenif any of the methods is applied to an optical scanning apparatus, it isimpossible to avoid to scale up the structure of the optical scanningapparatus. Also, there arise vibration, noise and heat in the opticalscanning apparatus. In addition, it is hard to drive the opticalscanning apparatus to which these methods are applied at a low voltage.

However, if the liquid crystal deflecting element 28 according to thefirst embodiment is used as the light path deflecting part fordeflecting an optical beam, it is possible to overcome theabove-mentioned problems.

FIGS. 5A and 5B show examples of the structure and a deflectingoperation of the liquid crystal deflecting element 28 according to thefirst embodiment, respectively. As is shown in FIG. 5A, the liquidcrystal deflecting element 28 comprises two transparent glass substrates28-1 on which transparent electrodes 28-2 and orientation films 28-3 areprovided, spacers 28-4 and liquid crystal 28-5. The spacers 28-4 areprovided between the two glass substrates 28-1 so that two orientationfilms 28-3 can be opposed to each other and the liquid crystal 28-5 canbe filled between the two glass substrates 28-1. When the transparentelectrodes 28-2 are connected to a driving control system 28-6 and arectangular wave or a sine wave is supplied thereto as a drivingvoltage, an optical beam can be deflected as shown in FIG. 5B. Also, itis possible to adjust the deflection angle by varying duty or amplitudeof the rectangular wave or the sine wave.

If an optical beam is required to increase deflecting response speed sothat the optical beam can correspond to the rotational irregularity of aphotoreceptor drum, the liquid crystal element 28 has to be formed of aplurality of liquid crystal layers. If the optical beam does not have tohave such high deflecting response speed, the liquid crystal element 28may be formed of a single liquid crystal layer.

Here, the beam pitch PY, which is an interval between beam spots withrespect to the main scanning direction on the scanned surface 16, isgiven as follows;PY=FY×θ,where FY represents focus length of the optical scanning system withrespect to the main scanning direction. If the liquid crystal deflectingelement 28 deflects both or either of the two optical beams 21 a and 21b so as to change the angle θ between the two optical beams 21 a and 21b as an angle Δθ in the main scanning section, the angle θ in the aboveformula is set as an angle θ+Δθ. As a result, it is possible to set thebeam pitch PY with respect to the main scanning direction as a desiredvalue.

In other words, if at least one of the two optical beams isindependently deflected in the main scanning direction and thesubscanning direction, it is possible to freely adjust alignment of beamspots on the scanned surface 16.

Here, the liquid crystal deflection element 28 may have a single body ormay have a two-layer body.

In FIG. 1, the liquid crystal elements 28 a and 28 b of the liquidcrystal deflecting element 28 are separately provided to the two opticalbeams.

In contrast, as is shown in FIG. 6, when the liquid crystal deflectingelement 28 formed of a single liquid crystal element is divided into aplurality of domains or effective areas (two domains in FIG. 6) asmentioned later, it is possible to modulate the effective areasseparately. As a result, it is possible to reduce the number of parts ofthe liquid crystal deflecting element 28 and position the liquid crystaldeflecting element 28 with high accuracy. Furthermore, it is possible tosimplify wirings to input an electronic signal.

Here, a supplemental description will be given of the structure and adeflecting operation of a liquid crystal deflecting element that theoptical scanning apparatus according to the first embodiment can adopt.

Typically, there are two types of liquid crystal deflecting elements.One is a liquid crystal deflecting element driven by an electronicsignal. The other is a liquid crystal deflecting element driven by amagnetic signal. The following description concentrates on an electronicsignal driven type liquid crystal deflecting element. The electronicsignal driven type liquid crystal deflecting element is furtherclassified into two types based on operations thereof. One is a liquidcrystal deflecting element that changes the refractive index through anelectronic signal. The other is a liquid crystal deflecting element thatcauses diffraction through an electronic signal.

Japanese Laid-Open Patent Application No. 63-240533 discloses an opticaldeflector related to the former type liquid crystal deflecting elementfor deflecting a light path by changing the refractive index.

FIGS. 7A through 7C are diagrams for explaining an example of a liquidcrystal deflecting element for deflecting a light path by changing therefractive index through an electronic signal.

In FIG. 7B, liquid crystal 71 is formed of nematic liquid crystal havingpositive dielectric anisotropy. The liquid crystal 71 is sealed in athin film between two transparent orientation films 72 a and 72 b thatare located distantly at a predetermined interval by spacers 73. Theform of a liquid crystal molecule 71 a extends in the molecule axisdirection. The orientation film 72 a is processed so that the moleculeaxis of the liquid crystal molecule 71 a can be orthogonal with respectto the surface of the orientation film 72 a. In contrast, theorientation film 72 b is processed so that the molecule axis of theliquid crystal molecule 71 a can be parallel with respect to the surfaceof the orientation film 72 b.

A transparent electronic resistor layer 74 formed of ZnO and others isprovided on the opposite surface of the orientation film 72 a toward theliquid crystal 71. As is shown in FIG. 7B, the electronic resistor layer74, the orientation films 72 a and 72 b, and the liquid crystal 71 aresandwiched between transparent glass substrates 75 a and 75 b. Atransparent electrode film 76 formed of ITO and others covers theorientation film 72 b side surface on the glass substrate 75 b.

On the other hand, two electrodes 77 a and 77 b having patterns as shownin FIG. 7A are provided on the orientation film 72 a side surface of theglass substrate 75 a. As is shown in FIG. 7B, the electrodes 77 a and 77b have contacts with the electronic resistor film 74.

If the electrodes 77 a and 77 b are located in a transmission area of aluminous flux, the electrodes 77 a and 77 b need to be formed of ITO andothers as transparent electrodes. However, if the electrodes 77 a and 77b do not interrupt the luminous flux, the electrodes 77 a and 77 b maybe formed of a metal film and others as opaque electrodes. FIGS. 7Athrough 7C handle the case where the electrodes 77 a and 77 b are formedof transparent electrodes.

If the electrode film 76 and the electrode 77 b are grounded and avoltage V is applied between terminals A and B of the electrodes 77 aand 77 b as shown in FIG. 7A, an electric potential at the electronicresistor layer 74 linearly decreases from the electrode 77 a to theelectrode 77 b as shown in FIG. 7C. Between the electronic resistor film74 and the transparent electrode film 76, there arises a horizontaldirectional electric field that decreases linearly from the upper areato the lower area of FIG. 7B This electric field influences the liquidcrystal 71 and rotates the liquid crystal molecule 71 a so that themolecule axis can be parallel with the electric field. The liquidcrystal molecule 71 a has a rotation angle linearly proportionate to theintensity of the electric field. As a result, at the electrode 71 aside, the molecule axis of the liquid crystal molecule 71 a is directedclosely in the electric field direction, that is, the horizontaldirection in FIG. 7B. On the other hand, at the electrode 71 b side, themolecule axis of the liquid crystal molecule 71 a persists almostparallel with the electrode film 76 because the electric field hassubstantially intensity 0 at the electrode 71 b.

The dielectric constant of the liquid crystal molecule 71 a becomeslarge in the direction parallel with the molecule axis and small in thedirection orthogonal with the molecule axis. Thus, the refractive indexbecomes large in the direction parallel with the molecule axis. If therearises a distribution directing in the molecule axis direction under theinfluences by the electric field, the liquid crystal 71 has largerefractive index in the electrode 71 a side where the molecule axis isalmost parallel with the electric field. In contrast, the liquid crystal71 has small refractive index in the electrode 71 b side. As is shown inFIG. 7C, the refractive index decreases linearly from the electrode 71 aside to the electrode 71 b side.

Therefore, if an illuminant flux from the right side enters the liquidcrystal deflecting element having a refractive index distribution inorder to transmit the liquid crystal deflecting element, the transmittedilluminant flux is deflected in the high refractive index side, that is,the upper direction in FIG. 7B, due to the influence of the refractiveindex distribution.

To the contrary, if the grounded electrode is replaced with theelectrode 77 a and a voltage V is applied between the two terminals Aand B in the inverse direction, there arises a refractive indexdistribution where the electric potential at the electronic resistorfilm 74 decreases from the electrode 71 b to the electrode 71 a. As aresult, it is possible to deflect the transmitted illuminant flux in thelower direction in FIG. 7B.

The principle of illuminant flux deflection by means of the liquidcrystal deflecting element that changes the refractive index has beendescribed in the above. However, a deflection angle, which is an amountof deflection, is saturated at an inherent value for the liquid crystaldeflecting element. Once the deflection angle is saturated, thedeflection angle never exceeds the saturated value. Although the liquidcrystal deflecting element may be driven by an electronic signal of adirect voltage, it is preferable that the electronic signal is modulatedin a pulse form or a sine wave form and the average voltage isapproximate 0V from the viewpoint of the duration thereof.

Although the deflection angle is changed by adjusting the electricpotential difference V between the terminals A and B, the deflectionangle may be changed by adjusting the duty ratio of the pulse if thepulse signal is used as a driving signal as mentioned above.

If a liquid crystal deflection element as shown in FIG. 1 has the largeinterval between the electrodes 71 a and 71 b, there arises nodiffraction light.

FIGS. 8A through 8C are diagrams for explaining another example of aliquid crystal deflecting element that changes the refractive index withan electronic signal wherein parts similar to those parts in FIGS. 7Athrough 7C are designated by the same reference numerals for simplicity.This liquid crystal deflecting element is a variation of that in FIGS.7A through 7C. The liquid crystal deflecting element differs in that atransparent electronic resistor film on the glass substrate 75 a isdivided into three parts 74 a, 74 b and 74 c and the transparentelectrode has the pattern as shown in FIG. 8A. Here, the electronicresistor films 74 a, 74 b and 74 c correspond to a pair of transparentelectrodes 77 a 1 and 77 b 1, a pair of transparent electrodes 77 a 2and 77 b 2, and a pair of transparent electrodes 77 a 3 and 77 b 3,respectively.

If a driving signal is applied between the terminals A and B, therefractive index distribution as shown in FIG. 8C is obtained. In thiscase, the rate of intensity change of the electric field to the voltageV between the terminals A and B becomes high. Thus, this liquid crystaldeflecting element has a larger gradient of the refractive index and alarger deflection angle than that in FIGS. 7A through 7C.

In the liquid crystal deflecting element in FIGS. 8A through 8C, as thenumber of combinations of electronic resistors and electrodes associatedwith the electronic resistors, for instance, a combination of theelectronic resistor film 74 a and the pair of the electrodes 77 a 1 and77 a 1, increases, the deflection angle becomes large. In this case,however, each period with respect to the combinations becomes shorter asshown in FIG. 8C. As a result, there arises diffraction light.

FIGS. 9A and 9B are diagrams for explaining an example of a liquidcrystal deflecting element that causes diffraction by an electronicsignal wherein parts similar to those parts in FIGS. 7A through 7C aredesignated by the same reference numerals for simplicity.

Japanese Laid-Open Patent Application No. 08-313941 discloses an opticaldeflector related to such a liquid crystal deflecting element in detail.

In FIG. 9A, the liquid crystal 71 is formed of nematic liquid crystalhaving a negative dielectric anisotropy wherein the liquid crystalmolecule 71 a therein has a smaller dielectric constant in the moleculeaxis direction than the direction orthogonal to the molecule axis. Theliquid crystal 71 is sealed in a thin layer form between two transparentorientation films 72 a and 72 b that are provided distantly at apredetermined interval by means of spacers 73.

The orientation films 72 a and 72 b are sandwiched between the glasssubstrate 75 a having the transparent electrode 76 a and the glasssubstrate 75 b having the transparent electrode 76 b. The transparentelectrodes 76 a and 76 b are formed of ITO and others in a thin filmform. The transparent electrodes 76 a and 76 b are uniformly provided onthe surfaces of the glass substrates 75 a and 75 b in a predeterminedshape, respectively.

The orientation films 72 a and 72 b provides an orientation to theliquid crystal 71 so that the molecule axis direction of the liquidcrystal molecule 71 a can be orthogonal to the sheet of FIG. 9A.

In this configuration, if a direct voltage or a low-frequency voltageless than about 300 Hz is applied between the transparent electrodes 76a and 76 b, the liquid crystal 71 has a diffraction lattice pattern ofthe vertical direction of FIG. 9A, that is, the direction orthogonal tothe above-mentioned orientation. FIG. 9B shows the refractive indexdistribution in the diffraction lattice pattern.

Here, if an illuminant flux enters the liquid crystal deflectingelement, the transmitted light causes diffraction light in the verticaldirection in FIG. 9A under the influence of the diffraction latticepattern. It is possible to change the lattice pitch of the diffractionlattice pattern and the diffraction angle by varying the level of thelow-frequency voltage.

Thus, if the deflection angle of the first order diffraction light isadjusted, it is possible to deflect an illuminant flux at a desireddeflection angle in a desired direction.

In contrast, if a high-frequency voltage is applied between thetransparent electrodes 76 a and 76 b in the liquid crystal deflectingelement in FIG. 9A, there arises a diffraction lattice pattern in thedirection orthogonal to the orientation direction of the liquid crystal71. As a result, it is possible to obtain diffraction light in thedirection orthogonal to the sheet of FIG. 9A. In this case, it ispossible to obtain various diffraction angles by changing an envelopevoltage of the high-frequency voltage.

The conventional liquid crystal deflecting element for deflecting anilluminant flux by an electronic signal has been described in the above.

The optical scanning apparatus according to the first embodiment usessuch a conventional liquid crystal deflecting element as the light pathdeflecting part thereof to adjust optical spots through deflection of anilluminant flux. However, the light path deflecting part according tothe embodiment is not limited to such a conventional liquid crystaldeflecting element for deflecting an illuminant flux by an electronicsignal. The liquid crystal deflecting element may be driven by amagnetic signal, which is not described above.

FIG. 6 is a perspective view of only an optical system being in theupper stream of the optical deflector in the optical scanning apparatusaccording to the present invention. The other parts being in the lowerstream of the optical deflector have the same structure as that of FIG.1.

Like the optical scanning apparatus in FIG. 1, an illuminant apparatus18 in FIG. 6 comprises at least semiconductor lasers 11 a and 11 b andcoupling lenses 12 a and 12 b. However, the illuminant apparatus 18 isnot limited to this configuration. Also, the semiconductor lasers 11 aand 11 b may be formed of a single beam semiconductor laser having onlyone illuminant point or a multi-beam semiconductor laser (semiconductorlaser array) having a plurality of illuminant points.

Laser light emitted from the semiconductor lasers 11 a and 11 b iscoupled by the coupling lenses 12 a and 12 b in order to form twooptical beams (laser beams) 21 a and 21 b. The two optical beamsapproach to each other and then is synthesized by a beam synthesizingprism 17 serving as a beam synthesizing part of the optical scanningapparatus.

The optical scanning apparatus having this configuration has someadvantages. First, it is possible to position the illuminant moreflexibly. Second, it is possible to make a cross angle θ smaller whereinthe cross angle θ of two optical beams is determined with respect to themain scanning section around a deflecting reflection surface of thepolygon mirror 14. Third, it is possible to integrally provide a controlsubstrate for driving/controlling two semiconductor lasers.

In addition, when the illuminant apparatus comprises the semiconductorlasers 11 a and 11 b and the coupling lenses 12 a and 12 b, it ispossible to easily obtain optical beam characteristics such as collimateproperty and optical axis direction in accordance with an optical systembeing in the lower stream of the optical deflector.

As is shown in FIG. 10, it is possible to adjust positions of thecoupling lens 12 a and 12 b toward the semiconductor lasers 11 a and 11b and then is fixed to the retention member 22 by using an ultravioletsensitive adhesive through visual examination of beam characteristics ofthe optical beam 21 emitted from the semiconductor laser 11 mounted to aholding member 22.

As is shown in FIG. 11, a male screw part of a lens cell 23 includingthe coupling lens 12 is joined to a female screw part of a holder member24 so as to adjust positions of the semiconductors 11 a and 11 b withrespect to the X direction (the horizontal direction in FIG. 11), thatis, to adjust the collimate ratio. At the same time, positions of thesemiconductor lasers 11 a and 11 b mounted to a base member 25 areadjusted with respect to the Y and Z directions (the vertical directionin FIG. 11 and the perpendicular direction to the sheet of FIG. 11). Inother word, the projection direction of an optical beam is adjusted.

Such adjustment of the relative positions of the semiconductor laserswith the coupling lens is generally called “optical axis/collimateadjustment”.

As is shown in FIG. 12, there is a probability that there arises anerror (an optical axis deviation: e) on synthesis accuracy of theoptical beams 21 a and 21 b due to fabrication error and part errorrelated to the inner refractive index of a beam synthesizing part (beamsynthesizing prism 17). Furthermore, there may arise a differencebetween a desired value and an actual value with respect to the beamspot interval on the scanned surface 16 due to the optical axisdeviation e.

For instance, it is assumed that the optical axis deviation e arises inthe subscanning direction. In this case, the beam spot interval PZ withrespect to the subscanning direction on the scanned surface 16 has theerror ΔPZ in the following formula;ΔPZ=mZ×fcol×tan(e),where fcol is a focus distance of the coupling lens and mZ is asubscanning horizontal magnification of all the optical scanning systemsfrom the illuminant to the scanned surface. In this formula, if mz=10,fcol=15 [mm] and e=2.9 [mrad], the error ΔPZ is obtained as follows;ΔPZ=10×15×tan(2.9×10−3)=0.436 [mm].

Even if the beam synthesizing part has such synthesis accuracy, it ispossible to perform the above “optical axis/collimate adjustment” fornot only the illuminant but also the beam synthesizing part alltogether.

As is shown in FIG. 13, when the optical axis/collimate adjustment isperformed, for instance, the two optical beams 21 a and 21 b from thesemiconductor lasers 11 a and 11 b are projected to a position sensor 26for detecting the optical axis in a condition where the two opticalbeams 21 a and 21 b is passing through the beam synthesizing prism 17.As a result, it is possible to detect and correct an error caused byboth the illuminant and the beam synthesizing prism 17.

Here, when the optical axis/collimate adjustment is performed, thereoften arises adjustment error. However, it is possible to correct theoptical axis adjustment error by using the liquid crystal deflectingelement 28 in the light path as mentioned above.

In order to obtain a desired diameter of a beam spot on the scannedsurface 16, an aperture for shaping the optical beam is often providedin the middle of the light path. For instance, an aperture member 27having such apertures is provided in the upper stream (illuminant side)from the liquid crystal deflecting element 28 in the light path as shownin FIG. 13 and FIG. 14. As a result, it is possible to narrow aneffective area of the liquid crystal deflecting element 28, that is, tominiaturize the size of parts therein. In addition, it is possible tonarrow an optically satisfactory area in the liquid crystal deflectingelement 28. As a result, it is possible to simplify the manufacturingprocess and improve the yield of the liquid crystal deflecting element28.

Also, if the apertures for shaping the optical beam are formed on one ofthe entrance surface and the exit surface of the liquid crystaldeflecting element 28, it is not necessary to separately provide anaperture member. As a result, it is possible to reduce the number ofparts therein and position an aperture relatively to the effective areaof the liquid crystal deflecting element 28 with accuracy.

Here, a silk screen process printing technique or the like is used toform the aperture on the entrance surface and the exit surface of theliquid crystal deflecting element 28.

The relative position of the semiconductor lasers 11 a and 11 b to thecoupling lenses 12 a and 12 b fluctuates due to environmental changes(temperature, moisture and so on) and time passage. The fluctuationdeteriorates alignment accuracy of beam spots on the scanned surface 16.

In this case, a beam spot array detecting part for detecting alignmentof beam spots or scanning pitch on the scanned surface 16 is provided inthe optical scanning apparatus 20. When the liquid crystal deflectingelement 28 is driven/controlled (modulated) by an electronic signalbased on detection results, it is possible to correct the fluctuation ofthe beam spot interval. For instance, the beam spot array detecting partis provided instead of the synchronization detection plate 19 in FIG. 1.

The liquid crystal deflecting element 28 is driven/controlled through afeedback system so that the detected alignment of beam spots can belocated at a desired position. Also, if beam spot array fluctuationinformation due to the environmental variations and the time passage isavailable in advance, the liquid crystal deflecting element 28 may bedriven/controlled based on a fluctuation table in a memory in thecontrol system thereof.

Here, the beam spot array detecting part may be implemented with adetecting part of a multi-beam scanner according to Japanese Laid-OpenPatent Application No. 09-325288.

Also, if a detecting part such as CCD (Charge Coupled Diode) is usedinstead of the beam spot array detecting part 19, it is possible todetect not only alignment of beam spots (relative positions betweenindividual beam spots) on the scanned surface 16 but also absolutepositions of the individual beam spots. As a result, it is possible toadjust the absolute positions of the beam spots by driving/controllingthe liquid crystal deflecting element 28.

The optical scanning apparatus according to the first embodiment havebeen described heretofore. Although the description has concentrated onthe 2-beam scanning apparatus, simultaneously emitted optical beams maybe formed of a single beam or above three beams.

A description will now be given of an illuminant apparatus according tothe present invention.

In the following, the X direction, the Y direction and the Z directionrepresent the direction along a light path (optical axis), the mainscanning direction and the subscanning direction, respectively, like theabove-mentioned optical scanning apparatus. Also, although the mainscanning direction and the subscanning direction generally mean adirection where a beam spot scans a surface and a direction orthogonalto the main scanning direction, respectively, the main scanningdirection and the subscanning direction according to this embodimentmean the main scanning direction and the subscanning direction withrespect to individual spots in a light path, respectively.

FIG. 15 is a perspective view of the structure of an optical scanningapparatus according to this embodiment of the present invention. FIG. 16is a plan view of primary parts in the optical scanning apparatus withrespect to the main scanning section.

In FIG. 15 and FIG. 16, an illuminant apparatus 18 comprises twosemiconductor lasers 11 a and 11 b, two coupling lenses 12 a and 12 b,and light path deflecting parts 29 a and 29 b. However, the illuminantapparatus 18 is not limited to this configuration. Also, thesemiconductor lasers 11 a and 11 b may be formed of single beamsemiconductor lasers having only one illuminant point or may be formedof multi-beam semiconductor lasers (semiconductor laser arrays) having aplurality of illuminant points.

The optical beams 21 a and 21 b are shaped into a linear form by acylindrical lens 13, and the linear optical beam is projected on adeflecting reflection surface of a polygon mirror 14, which serves as adeflecting system for producing an optical beam that is concentrated onthe subscanning direction and is linearly formed with respect to themain scanning direction. Then, the deflected linear optical beam isprojected to a scanning optical system 15 comprising two scanning lenses15 a and 15 b and a reflecting mirror 15 c in order to provide beamspots for scanning a scanned surface 16, for instance, a photoreceptordrum.

In a case where an optical scanning apparatus 20 according to thisembodiment is used as an optical writing part of an image formingapparatus, an optical beam is modulated corresponding to output imagedata. When the synchronization detection plate (synchronizationdetecting sensor) 19 detects the optical beam, an electronic signal(synchronization signal) is provided as the modulation start timing.

The two optical beams 21 a and 21 b entering a deflector (polygonmirror) 14 are not parallel with each other.

In this configuration, it is possible to obtain an interval PY of twobeam spots on a scanned surface with respect to the main scanningdirection. As a result, it is possible to detect the synchronizationdetection signals for the two optical beams separately through just thesynchronization detection plate 19.

Conventionally, when the two optical beams are reflected on a deflectingreflection surface of the polygon mirror 14 and then enter an opticalscanning system 15, the optical beams are formed as parallel opticalfluxes, weak divergence optical fluxes or weak convergence opticalfluxes. These optical fluxes serve to form beam waists in the vicinityof the scanned surface 16. Thus, in the case where the two optical beamsentering the deflecting reflection mirror of the polygon mirror 14 areparallel with each other, that is, the case where the two optical beamsentering the optical scanning system 15 are parallel with each other,the two optical beams cross around the scanned surface 16, that is, thebeam pitch PY with respect to the main scanning direction becomes 0,under influences by the optical scanning system 15. As a result, it isimpossible to separately obtain the synchronization detection signal.

In FIG. 16, the two optical beams cross by the angle Θ (=2θ) around thedeflecting reflection surface of the polygon mirror 14, that is, the twooptical beams are not parallel with respect to the main scanningsection. Therefore, it is possible to not only separately detect thesynchronization detection signal but also suppress differences ofoptical characteristics such as field curvature and magnification errorsbetween the two optical beams.

Here, if the optical scanning system 15 can perform uniform scanningmotion (fθ characteristic), the beam spot interval with respect to themain scanning direction PY is as follows;PY=FY×Θ,where FY is a focus distance with respect to the main scanning directionof the optical scanning system 15.

For instance, if FY=220 [mm] and E=1°=0.01745 [rad], the beam spotinterval PY is given as follows;PY=FY×Θ=220×0.01745=3.8 [mm].

Therefore, even if a reasonable synchronization detection sensor isused, it is possible to separately detect the synchronization detectionsignals of the two optical beams.

As mentioned above, the two beam spots BS1 and BS2 are required tomaintain a predetermined interval (beam pitch: PZ) with respect to thesubscanning direction on the scanned surface 16 in accordance with thescanning density. In order to set the beam pitch PZ, it is necessary toadjust an angle φ between the two optical beams 21 a and 21 b as shownin FIG. 4. It is supposed that subscanning magnification of the entireoptical scanning system is notated by mZ and the focus distance of thecoupling lens is notated by fcol. Then, the beam spot pitch PZ is givenas follows;PZ=mZ×fcol×tan φ.

Since the angle φ is enough small, tan φ may approximate the value φ.Thus, the above formula is rewritten as follows;PZ=mZ×fcol×φ.

Here, there is a probability that the beam spot pitch PZ varies underthe influences by environmental fluctuations and time passage. Theilluminant apparatus according to this embodiment intends to correct thebeam spot pitch PZ.

As is shown in FIG. 15 and FIG. 16, an optical path deflecting part isintegrally formed of optical deflecting elements 29 a and 29 b that canbe individually controlled. The optical path deflecting part is providedin light paths of the two optical beams 21 a and 21 b. A wedge-shapedprism 30, which is to be mentioned later, is used as the light pathdeflecting element of the optical scanning apparatus shown in FIG. 15and FIG. 16.

FIG. 17 is an enlarged view of the light path deflecting element(wedge-shaped prism unit) formed of the wedge-shaped prism 30 being atransmission optical element.

In the light path deflecting element, the wedge-shaped prism 30 isinserted into a ring ultrasound motor 31 driven by a piezoelectricelement. When the ring ultrasound motor 31 causes rotation in thedirections shown by the arrow γ in FIG. 17, it is possible to deflectoptical beams in the directions as shown by the arrow φ, that is, todeflect the optical beams with respect to the subscanning direction.When two light path deflecting elements 29 a and 29 b formed of such awedge-shaped prism unit are mounted to the common holding member 29 asshown in FIG. 15 and FIG. 16, the two light path deflecting elements 29a and 29 b are integrated into the illuminant apparatus. As a result, itis possible to implement the illuminant apparatus 18 capable ofdeflecting an optical beam without increasing the size of the illuminantapparatus 18.

In the case where the above-mentioned ring ultrasound motor 31 is used,it is possible to not only adjust the light paths by the order of a nanometer nm or a micro meter μm but also maintain the adjusted conditioneven in power OFF because of strong retention of the holding member 29.

In the optical beam 21 a, if an angle of the wedge-shaped prism 30, aninternal refractive index, a rotational angle and a deflection angle arenotated as αa, na, γa and φa, respectively, the deflection angle φa iscomputed as follows;φa=(na−1)×αa×sin γa.Therefore, the moving distance Za of a beam spot on the scanned surfacecorresponding to the optical beam 21 a is given as follows;Za=mZ×fcol×φa=mZ×fcol×(na−1)×αa×sin γa.

For instance, it is supposed that na=1.5, mZ=9.5, fcol=15 [mm],αa=1°=0.01745 [rad]. In this supposition, the moving distance Za iscomputed as follows;

$\begin{matrix}{{Za} = {{{{mZ} \times {fcol} \times \phi}\; a} = {{{mZ} \times {fcol} \times \left( {{na} - 1} \right) \times \alpha}\;{a \times \sin}\;\gamma\; a}}} \\{= {{9.5 \times 15 \times \left( {1.5 - 1} \right) \times 0.01745 \times \sin}\;\gamma\; a}} \\{= {{1.24 \times \sin}\;\gamma\;{a.}}}\end{matrix}$If the angle γa changes from −90° to +90° here, the beam spot on thescanned surface moves by the distance ±1.24 [mm].

On the other hand, the moving distance Zb of a beam spot on the scannedsurface corresponding to the optical beam 21 b is computed as follows;Zb=mZ×fcol×φb=mZ×fcol×(nb−1)×αb×sin γb.

Here, if it is supposed that na=nb=n and αa=αb=α, the angle φ is givenas follows;φ=φa−φb=(n−1)×α×(sin γa−sin γb).

In the above formula, if the values γa and γb are appropriatelyprovided, it is possible to set PZ as a desired value. Here, in order todeflect the resulting optical beam, both of the two optical beams may bedeflected or one of the two optical beams may be deflected.

FIGS. 18A through 18C show an example where a cylindrical lens being thetransmission optical element is used as the light path deflecting partof the optical scanning apparatus according to the present invention.

As is shown in FIG. 18A, a lens holder 35 is provided between an elasticmember (coil spring) 34 and a piezoelectric element 32 in the inner sideof the holding member 29, and a cylindrical lens 33 is mounted to thelens holder 35. If a voltage is applied to the piezoelectric element 32,there arises displacement Δ as shown in FIG. 18C. Here, if thecylindrical lens 33 is shifted along the subscanning section in thedirection as shown by the arrow Z shown in FIG. 18B, it is possible todeflect an optical beam in the direction shown by the arrow φ.

When two light path deflecting elements 29 a and 29 b formed of thecylindrical lens units are mounted to the common holding member 29 asshown in FIG. 15 and FIG. 16 and are integrally provided to theilluminant apparatus 18, it is possible to implement the illuminantapparatus 18 capable of deflecting an optical beam without increasingthe size of the illuminant apparatus 18.

In the above-mentioned two examples related to the wedge-shaped prismand the cylindrical lens, a piezoelectric element works as an actuatorof the light path deflecting element. However, a pulse motor thatrotates by a predetermined angle through an input pulse signal may beused as the actuator of the light path deflecting element, or anothertype pulse motor that moves straight at a predetermined distance throughan input pulse signal may be used as the actuator thereof.

In such a pulse motor, since the angle can be changed proportionately tothe step number of the input pulse signal, it is possible to easilyobtain a desired adjustment value, in some cases, under open-loopcontrol. In addition, since a pulse motor is more popularly used than anultrasound motor at present, the pulse motor is available at reasonablecost. Thus, if the pulse motor is used as the actuator instead of theultrasound motor, it is possible to reduce fabrication cost of theilluminant apparatus.

A description will now be given, with reference to FIGS. 19A and 19B, ofanother light path deflecting element according to the presentinvention. A reflection optical element is used in the light pathdeflecting element of the optical scanning apparatus according to thisembodiment.

FIG. 19A shows an optical system being in the upper steam side of theoptical deflector 14 in the case where reflection optical elements areused as light path deflecting elements of the optical scanning apparatusshown in FIG. 15 and FIG. 16. FIG. 19B is an enlarged view of one of thelight path deflecting elements.

Reflection mirrors 37 a and 37 b are used in the light path deflectingelements. Since the piezoelectric element 32 causes displacementproportionate to an impressed voltage, the reflection mirror 37 mountedto a mirror holder 39 rotates on a roller 38 in the direction pointed atby the arrow β. As a result, it is possible to deflect an optical beamby the angle φ=2×β

Such reflection mirror units are mounted to the common holding member 29and are integrally provided to the illuminant apparatus 18.

When such a reflection optical element is used in the light pathdeflecting element, it is possible to set a larger beam deflection anglethan a transmission optical element. As a result, it is possible toextend an adjustment range of a beam spot position.

A description will now be given, with reference to FIGS. 20A and 20B, ofa light path deflecting element of the illuminant apparatus according tothe present invention. In this embodiment, a liquid crystal element(liquid crystal deflecting element) is used in the light path deflectingelement.

FIGS. 20A and 20B handle a 4-beam illuminant apparatus in which fouroptical beams from illuminants are synthesized by a beam synthesizingprism to be mentioned later. In FIG. 20A, a liquid crystal element 40driven by an electronic signal is provided in the upper stream side(illuminant side) of the beam synthesizing prism 17 in a light path as alight path deflecting element. A light transmission part of the liquidcrystal element 40 is divided into four parts and the four parts(effective areas) can be independently controlled. In FIG. 20B, fourliquid crystal elements 40 a through 40 d are mounted to the holdingmember 29.

If a plurality of photoreceptor drums as the scanned surface 16 havedistinct sensitivity characteristics (wavelength dependence),semiconductor lasers in the illuminant apparatus need to have distinctoscillation wavelength in accordance with the correspondingphotoreceptor drums. In this case, it is necessary to provide a liquidcrystal element having the wavelength dependence corresponding to theoscillation wavelength. If the liquid crystal elements 40 a through 40 dare mounted to the common holding member 29 as shown in FIG. 20B, it ispossible to freely deflect distinct laser beams.

In a liquid crystal element whose wavelength dependence is low, that is,which is applicable to a wide range of wavelength, one liquid crystalelement 40 can provide a plurality of effective areas each of which canindependently be modulated in accordance with individual optical beams.

Conventionally, light path deflecting means have been proposed based onthe following methods. The first method is related to a mechanicalapproach. In this method, for instance, an optical beam is deflected bymoving a mirror or a prism in the light path thereof. The second methodis related to an approach by means of an electrooptic element. In thismethod, an optical beam is deflected by using material characteristicsof an electrooptic element to change the refractive index of a prism.The third method is related to an approach by means of acousto-opticelement. In this method, for instance, an optical beam is deflected bygenerating a diffraction grating in a piezoelectric body through anultrasonic wave.

However, any of these methods has some disadvantages. For instance, whenthe methods are applied to an illuminant apparatus, it is impossible toavoid to scale up the structure thereof. Also, there arise vibration,noise and heat in the illuminant apparatus. In addition, it is hard todrive the illuminant apparatus at a low voltage.

However, when a light path deflecting element (liquid crystal deflectingelement) formed of the liquid crystal elements 40 a through 40 d is usedas a light path deflecting part for deflecting an optical beam, it ispossible to miniaturize an illuminant apparatus having such a light pathdeflecting element, suppress vibration and the like, and drive theilluminant apparatus at a low voltage.

Here, the detailed description of the liquid crystal element is omittedbecause the liquid crystal deflecting element according to thisembodiment is similar to the liquid crystal deflecting element providedin FIGS. 5A and 5B or a conventional liquid crystal element describedwith reference to FIG. 7 through FIG. 9.

FIG. 21 is a perspective view of another illuminant apparatus accordingto the present invention wherein the illuminant apparatus has thesimilar structure of the lower stream of the cylindrical lens 13 to thatin FIG. 15.

As is shown in FIG. 21, the illuminant apparatus comprises a firstilluminant part 41 formed of at least two pairs of a semiconductor laser11 a and the corresponding coupling lens 12 a and a semiconductor laser11 b and the corresponding coupling lens 12 b and a base member 43 a forintegrally holding these parts in one line in the main scanningdirection, a second illuminant part 42 formed of at least two pairs of asemiconductor laser 11 c and the corresponding coupling lens 12 c and asemiconductor laser 11 d and the corresponding coupling lens 12 d and abase member 43 b for integrally holding these parts in one line in themain scanning direction, a beam synthesizing part (beam synthesizingprism) 17 for synthesizing a plurality of optical beams emitted from thefirst and the second illuminant parts 41 and 42 and emitting thesynthesized optical beams, and a light path deflecting element 40 suchas a liquid crystal element provided between the first and the secondilluminant parts 41 and 42 and the beam synthesizing part 17.

Laser light emitted from four semiconductor lasers 11 a through 11 d arecoupled by the corresponding coupling lenses 12 a through 12 d to befour optical beams 21 a through 21 d. The two beams 21 a and 21 bemitted from the first illuminant part 41 approach the two beams 21 cand 21 d emitted from the second illuminant part 42 and then the fourbeams are synthesized by the beam synthesizing prism 17.

The illuminant apparatus according to this configuration has someadvantages. First, the illuminants can be positioned more flexibly.Second, it is possible to make the cross angle Θ between the two opticalbeams smaller with respect to the main scanning section around adeflecting reflection surface of the polygon mirror 14. Third, it ispossible to integrally provide a control substrate fordriving/controlling the four semiconductor lasers. Fourth, when theilluminant apparatus and the optical scanning apparatus according tothis embodiment are assembled, it is possible to easily adjust the beampitch on the scanned surface with respect to the subscanning direction.

The base members 43 a and 43 b are fixed to a flange 44 with a screw 45and a washer 46. Also, the liquid crystal element 40 is fixed to theflange 44 with some adhesive processes. The beam synthesizing prism 17is fixed to another holding member that is not illustrated.

A liquid crystal element can be used as a light path deflecting elementin the 4-beam illuminant apparatus like FIGS. 20A and 20B. FIGS. 22A and22B show an example of a 4-beam illuminant apparatus in which awedge-shaped prism is used as a light path deflecting element.

In FIGS. 22A and 22B, a plurality of wedge-shaped prisms (light pathdeflecting elements) 30 a through 30 d are mounted to the common holdingmember 29 via ring ultrasound motors 31 a through 31 d similarly to FIG.17.

When the ring ultrasound motors 31 a through 31 d separately rotate thewedge-shaped prism 30 a through 30 d, it is possible to independentlyadjust positions of four beam spots on the scanned surface 16.

Here, whichever type of light path deflecting element is used, all thefour beam spots are not adjusted in the above-mentioned fashion. If oneof the four beam spots is specified as a reference beam spot, the otherthree beam spots may be adjusted relatively to the reference beam spot.In this case, it is possible to omit the beam deflecting elementcorresponding to the reference beam spot and the actuator for drivingthe beam deflecting element.

FIG. 23A shows an example of an optical scanning apparatus where theilluminant apparatus shown in FIG. 21 are combined with an opticalscanning system. FIG. 23B shows an example of alignment of beam spots onthe scanned surface 16.

In this configuration shown in FIG. 23A, it is not necessary to positionlight paths prior to the optical deflector in parallel with each otherin order to secure intervals Q1 through Q3 in the main scanningdirection of beam spots BSa through BSd on the scanned surface 16. As isshown in FIG. 23A, for instance, the cross angles Θ1 through Θ3 are setto cross the four optical beams around the deflecting reflection surfaceof the optical deflector 14. Then, the relationship between the crossangles and the intervals satisfies the following formula;Qj=FY×Θj (j=1, 2, 3).

In addition, if the illuminant apparatus is formed of semiconductorlasers and coupling lenses as mentioned above, it is possible to easilygain optical beam characteristics such as collimate property and opticalaxis direction in accordance with the optical system in the lowerstream.

As is shown in FIG. 10, for instance, the positions of the couplinglenses 12 a through 12 d are adjusted toward the semiconductor lasers 11a through 11 d based on observation results of beam characteristicsregarding the optical beams 21 a through 21 d emitted from thesemiconductor lasers 11 a through 11 d mounted to the base member 22 asmentioned in FIG. 10. Then, the coupling lenses 12 a through 12 d arefixed to the base member 25 by using ultraviolet sensitive adhesive. Asa result, it is possible to easily gain optical beam characteristics.

Furthermore, as is shown in FIG. 11, the relative position is adjustedwith respect to the X direction (horizontal direction in FIG. 10;collimate adjustment) by joining a male screw of the lens cell 23including the coupling lens 12 to a female screw of the holder member24. The relative positions of the semiconductor lasers 11 a through 11 dare adjusted with respect to the Y direction and the Z direction.

Such adjustment of the relative positions between the semiconductorlasers and the coupling lenses is often called optical axis/collimateadjustment. In general, the optical axis/collimate adjustment entails anadjustment error. However, if a light path deflecting element accordingto this embodiment is provided in a light path, it is possible tocorrect the optical axis adjustment error.

Furthermore, as is shown in FIG. 24, if the optical axis of the couplinglens 12 c (12 d) is shifted by the distance δz from the projection axisof the semiconductor laser 11 c (11 d), it is possible to set theoptical axis having the angle φ with respect to the subscanningdirection. The relationship between δz and φ is represented as follows;δz=fcol×tan φ,where fcol is the focus distance of the coupling lens 12 c (12 d).

Here, the above-mentioned semiconductor laser may be formed of a singlebeam semiconductor laser having a single illuminant point or may beformed of a multi-beam semiconductor laser (semiconductor laser array)having a plurality of illuminant points.

In order to obtain a desired diameter of a beam spot on the scannedsurface, an optical beam is often shaped by providing an aperture in themiddle of the light path. As is shown in FIG. 25, an aperture member 27having such an aperture is provided in the upper stream side (illuminantside) of a light path deflecting element such as a liquid crystalelement 40 in the light path of the optical beam.

In this configuration, it is possible to narrow an effective area of thelight path deflecting element, that is, to avoid to increase the size ofparts. Furthermore, it is possible to narrow an optically satisfactoryarea in the light path deflecting element 40, that is, to simplify thefabrication process and improve the yield of the fabrication process.

In addition, if the light path deflecting element such as the liquidcrystal element 40 does not move (parallel shift and rotation), it isunnecessary to add the above-mentioned aperture member for shaping anoptical beam on the entrance surface or the exit surface of the lightpath deflecting element. As a result, it is possible to reduce thenumber of parts and accurately position the aperture relatively to theeffective area of the light path deflecting element.

The aperture can be provided on the entrance surface and the exitsurface of the light path deflecting element by using silk screenprinting method and the like.

When the relative positions (adjustment value) between individualsemiconductor lasers and coupling lenses vary under influences byenvironmental changes and time passage, there is a probability thatmisalignment of beam spots arises on the scanned surface.

Even in this case, if a beam spot array detecting part for detectingpositions of the beam spots or the scanning line pitch on the scannedsurface 16 is provided in the optical scanning apparatus including theabove-mentioned illuminant apparatus and an optical beam deflectingelement is driven/controlled (modulate) by an electronic signal based ondetection results, it is possible to correct variations of the beam spotpitch.

Such a beam spot array detecting part can be provided instead of thesynchronization detection plate 19 in FIG. 15.

The light path deflecting element may be driven/controlled through afeedback system so that the beam spot array can have a desired value.Also, when correspondence information between the environmentalchanges/time passage and the beam spot array variations is obtained inadvance, the correspondence table in which variations of the beam spotarray are described for individual types of the environmental changesand amounts of the elapsed time is prepared in a memory of the controlsystem of the apparatus. Based on the correspondence table, the lightpath deflecting element may be driven/controlled.

The beam spot array detecting part 19 can be implemented with adetecting part of a multi-beam scanning apparatus according to JapaneseLaid-Open Patent Application No. 09-325288.

Also, if a detecting part of CCD is used as the beam spot arraydetecting part 19, it is possible to detect not only the beam spot array(relative positions between individual beam spots) on the scannedsurface 16 but also absolute positions of the individual beam spots. Asa result, the absolute positions of the beam spots can be adjusted bydriving/controlling the light path deflecting element.

In the above description, the 2-beam illuminant apparatus and the 2-beamscanning apparatus and the 4-beam illuminant apparatus and the 4-beamscanning apparatus have been described. However, the illuminantapparatus and the optical scanning apparatus according to the presentinvention may have an arbitrary number of optical beams.

A description will now be given of another optical scanning apparatusaccording to the present invention.

In the following, the X direction, the Y direction and the Z directionrepresent the direction along a light path (optical axis), the mainscanning direction and the subscanning direction, respectively, like thefirst and the second embodiments. Also, although the main scanningdirection and the subscanning direction generally mean the directionwhere a beam spot scans a surface and the direction orthogonal to themain scanning direction, respectively, the main scanning direction andthe subscanning direction in this embodiment mean the main scanningdirection and the subscanning direction with respect to individual spotsin a light path, respectively.

FIG. 26A is a perspective view of an optical scanning apparatusaccording to this embodiment. FIG. 26B is a perspective view of anilluminant apparatus according to this embodiment wherein a beamsynthesizing prism 17 is provided behind a coupling lenses 12 a and 12 bas the beam synthesizing part.

In FIGS. 26A and 26B, the illuminant apparatus 18 comprises at least twopairs of the semiconductor laser 11 a and the coupling lens 12 a and thesemiconductor laser 11 b and the coupling lens 12 b. However, theilluminant apparatus 18 is not limited to this configuration. Also, thesemiconductor lasers 11 a and 11 b may be formed of a single beamsemiconductor laser having a single illuminant point or be formed of amulti-beam semiconductor laser (semiconductor laser array) having aplurality of illuminant points.

Laser light emitted from the semiconductor lasers 11 a and 11 b arecoupled by the coupling lenses 12 a and 12 b to be two optical beams(laser beams) 21 a and 21 b.

The optical beams 21 a and 21 b are shaped into a linear form by acylindrical lens 13, and the linear optical beams are projected on adeflecting reflection surface of a polygon mirror 14, which serves as adeflecting system, in order to produce optical beams that areconcentrated on the subscanning direction and are linearly formed withrespect to the main scanning direction. Then, the deflected linearoptical beams are projected to an optical scanning system 15. Theoptical scanning system 15 comprises two scanning lenses 15 a and 15 band a reflecting mirror 15 c in order to provide a beam spot forscanning a scanned surface 16, for instance, a photoreceptor drum.

In a case where an optical scanning apparatus 20 according to thisembodiment is used as an optical writing apparatus in an image outputapparatus, an optical beam is modulated corresponding to output imagedata. When the optical beam enters a synchronization detection plate(synchronization detecting sensor) 19, an electronic signal(synchronization signal) is provided as the modulation start timingsignal.

Although the illuminant apparatus in FIG. 26A has no beam synthesizingpart such as the beam synthesizing prism 17 unlike that in FIG. 26B, twooptical beams cross by the angle Θ around a deflecting reflectionsurface of the polygon mirror 14. Thus, the illuminant apparatus in FIG.26A is considered to have the beam synthesizing part in a broad sense.Furthermore, in this illuminant apparatus, it is possible to not onlyseparately detect a synchronization detection signal but also reducedifferences of optical characteristics such as curvature field andmagnification error between two optical beams.

In FIG. 26A, an optical scanning apparatus has a light path deflectingpart behind the coupling lenses 12 a and 12 b so as to control positionsof the optical beams on the scanned surface 16.

Although liquid crystal elements (liquid crystal deflecting elements) 40a and 40 b controlled by an electronic signal are used as the light pathdeflecting part of the optical scanning apparatus in FIG. 26A, opticalbeams are deflected by driving the liquid crystal deflecting elements 40a and 40 b in order to control beam spot positions on the scannedsurface 16. Here, the liquid crystal elements may be separately providedas shown in FIG. 26A or be integrally provided as shown in FIG. 26B.

FIG. 27 shows an example of the structure of a liquid crystal deflectingelement 40. The liquid crystal deflecting element 40 comprises twotransparent glass substrates 40-1 on which transparent electrodes 40-2and orientation films 40-3 are formed, spacers 40-4, and liquid crystal40-5. The two glass substrates 40-1 are provided so that the orientationfilms can face on each other. The spacers 40-4 are provided between theglass substrates 40-1. The liquid crystal 40-5 fills the space betweenthe two glass substrates 40-1. A drive control system 40-6 is connectedto the transparent electrodes 40-2. When a rectangular wave or a sinewave is applied as a driving voltage, an optical beam can be deflected.Furthermore, if the rectangular wave or the sine wave has variable dutyor oscillation, it is possible to adjust the deflection angle. Here,when a liquid crystal element is used as the liquid crystal deflectingelement, the liquid crystal deflecting element can be preferablyimplemented with the above-mentioned liquid crystal deflecting elementprovided in FIG. 7 through FIG. 9.

In a case where the liquid crystal element 40 is used as a light pathdeflecting part to control beam spot positions on the scanned surface16, when the beam spot positions are to be moved by ΔZ in thesubscanning direction, it is necessary to set the beam deflection angleφZ with respect to the subscanning direction as follows;φZ=tan⁻¹(ΔZ/fcol×mZ)

This formula is transformed from the following formula;ΔZ=fcol×mZ×tan φz.

In contrast, when the beam spot positions are to be moved by Δy in themain scanning direction, it is necessary to set the beam deflectionangle φY with respect to the main scanning direction as follows;φY=tan⁻¹(ΔY/fcol×mY)=tan⁻¹(ΔY/FY).

Meanwhile, the optical scanning apparatus in FIG. 26A has the samestructure as the optical scanning apparatus in FIG. 1. If the liquidcrystal elements 40 a and 40 b are used as a light path deflecting partto deflect a light path, it is possible to easily adjust (correct) thebeam spot positions on the scanned surface 16. In addition, it ispossible to correct the beam spot positions even if the beam spotpositions vary under influences by temperature fluctuations and timepassage. Furthermore, the optical scanning apparatus has some advantagessuch as less light loss and low driving electric power.

On the other hand, a liquid crystal element 40 generally has a problemin that ghost light tends to arise due to diffraction. Liquid crystalelements are roughly divided into the following two types. The firsttype of liquid crystal elements generates a refractive indexdistribution by applying a voltage to a plurality of electrodes anddeflects incident light due to prism effect. The second type of liquidcrystal elements generates a striped pattern as a diffraction lattice byapplying a voltage to a plurality of electrodes. In this case, theincident light is deflected due to diffraction effect. In any type, itis usually possible to generate diffraction light corresponding to theelectrode pitch because the electrodes are provided in an electrodepattern so that the individual electrodes can be located in equalintervals.

FIG. 27 shows an example of ghost light in the liquid crystal element40. In the liquid crystal element 40, when diffraction light isgenerated by transparent electrodes 40-2 of the liquid crystal element40, the 0-order light of the diffraction light is deflected as writedata. On the other hand, the ±1-order light, the ±2-order light, . . .of the diffraction light are considered as unnecessary ghost light. Ifsuch ghost light appears on the scanned surface 16, an image may includea ghost image. As a result, the image is likely to deteriorate.

In order to remove the ghost light, a ghost light removing part 51 suchas a slit aperture is provided between the liquid crystal element 40 andthe deflector 14 as shown in FIG. 28.

When the slit aperture 51 is provided as the ghost light removing part,it is possible to easily remove harmful ghost light such as the ±1-orderlight, the ±2-order light, . . . that are generated by diffraction ofthe liquid crystal element 40.

Here, the slit aperture 51 may be formed of any shape such as arectangular aperture and an aperture formed by closing two lightshielding plate, that is, an aperture that is infinitely opened in thelongitudinal direction as long as the slit aperture 51 has an aperturein which ghost light is interrupted in the deflection direction of theliquid crystal element 40. Also, the slit aperture 51 may be formed bycovering a light shielding film or depositing an evaporated lightshielding material on a transparent member such as a glass plate. Also,the slit aperture 51 may be formed by making a rectangular hole on aplane plate by means of a knife-edge. Furthermore, the ghost lightshielding member may be provided such that the upper knife edge and thelower knife edge can be mounted at different places with respect to theoptical direction.

As is shown in FIG. 28, if the slit aperture 51 satisfies the followingformula, it is possible to reduce the ghost light efficiently;L≧(b+Δ)/(2×tan θ),where b is the width of an optical beam deflected by a liquid crystalelement, Δ is the width of a slit aperture, L is the distance betweenthe liquid crystal element and the slit aperture, and 2θ is an anglebetween +1st-order light and −1st-order light of the ghost lightgenerated by the liquid crystal element.

Here, the ghost light removing part such as the silt aperture 51 may beprovided in the upper stream side (the illuminant side) of the beamsynthesizing part or the lower stream (the scanned surface side) of thebeam synthesizing part.

FIG. 29A is a perspective view of another optical scanning apparatusaccording to the present invention. The optical scanning apparatusbasically has the same structure as that in FIG. 26A wherein the opticalscanning apparatus in FIG. 29A has an eccentric transmission opticalelement as the light path deflecting part.

FIG. 29B is a sectional view of the light path deflecting part(wedge-shaped prism unit) formed of transmission optical elements,wedge-shaped prisms 30 a and 30 b.

The optical scanning apparatus in FIGS. 29A and 29B basically has thesame structure as the optical scanning apparatus in FIGS. 26A and 26B.In the optical scanning apparatus in FIGS. 29A and 29B, the light pathdeflecting part can deflect an optical beam in the direction pointed atby the arrow φ in FIG. 29B, that is, the light path deflecting part canchange the optical beam with respect to the subscanning direction, byinserting the wedge-shaped prism 30 into the ring ultrasound motor 31driven by a piezoelectric element and rotating the wedge-shaped prism 30in the direction pointed at by the arrow y in FIG. 29B. If such twowedge-shaped prism units are mounted to the common holding member 29, itis possible to realize a light path deflecting part capable ofdeflecting an optical beam without the size increase.

When the wedge-shaped prism 30 a and 30 b are used as the light pathdeflecting part, it is possible to suppress generation of ghost lightunlike the above-mentioned optical scanning apparatus in which a liquidcrystal element is used as the light path deflecting part. As a result,it is unnecessary to install a ghost light removing part.

FIG. 30 is a plan view of another optical scanning apparatus accordingto the present invention. The optical scanning apparatus is accommodatedin an optical housing.

As is shown in FIG. 30, two illuminant modules 41 and 42 for emittingoptical beams are mounted on side walls of an optical housing 53 of theoptical scanning apparatus. The two optical beams 21 a and 21 b from theilluminant modules 41 and 42 are synthesized by an optical beamsynthesizing prism 17, and the synthesized optical beam enters thedeflector 14 formed of a polygon mirror via the cylindrical lens 13. Thelight path deflecting part 50 between the optical beam synthesizingprism 17 and the deflector 14 and the optical beam synthesizing prism 17are fixed to the common holding member 52.

In the optical scanning apparatus in FIG. 30, the two illuminant modules41 and 42 serve as the illuminant part such as a pair of a semiconductorlaser and a coupling lens. However, the illuminant part and the couplinglens are not necessarily integrated.

In addition, the illuminant modules 41 and 42 are not necessarily fixedto the side wall 54 of the optical housing 53. For instance, theilluminant modules 41 and 42 may be accommodated in the interior of theoptical housing 53 via bracket members.

If the optical scanning apparatus adopts the above-mentioned structure,it is possible to more easily replace a badly-performed illuminant orsemiconductor laser with the smaller number of parts than the opticalscanning apparatus shown in FIG. 21.

Furthermore, the ghost light removing part such as the slit aperture 51in FIG. 28 is often provided in the lower stream side (the deflectorside) of the optical beam synthesizing prism 17. However, even if thelight path deflecting part 50 is provided in the upper stream (theilluminant side) of the beam synthesizing prism 17, the ghost lightremoving part may be provided in the upper stream (the illuminant side)of the beam synthesizing prism 17 as long as such a layout is feasible.

FIGS. 31A and 31B show another optical scanning apparatus according tothe present invention.

FIG. 31A is a sectional view of an optical system fixed to an opticalhousing wherein an illuminant apparatus comprises at least twoilluminant modules 41 and 42 and a holding member 55 for holding theilluminant modules 41 and 42.

The two illuminant modules 41 and 42 may comprise a first i. Nalluminantmodule and a second illuminant modulemely, the first illuminant module41 comprises semiconductor lasers 11 a and 11 b, coupling lenses 12 aand 12 b, and a base member 43 a for integrally holding thesemiconductor lasers 11 a and 11 b and the coupling lenses 12 a and 12 bin lines in the main scanning direction. The second illuminant module 42comprises semiconductor lasers 11 c and 11 d, coupling lenses 12 c and12 d, and a base member 43 b for integrally holding the semiconductorlasers 11 c and 11 d and the coupling lenses 12 c and 12 d in lines inthe main scanning direction.

Although the optical system in FIG. 31A is formed as a 4-beam scanningapparatus, it is possible to provide a multi-beam scanning apparatusmore than 4 beams by increasing the number of illuminant modules or thenumber of emitted beams per one illuminant module.

FIG. 32 shows a variation of the optical system in FIG. 31A. As is shownin FIG. 32, the two illuminant modules 41 and 42 may be directly fixedon a side wall 54 of the optical housing 53 without use of the holdingmember 55.

A description will now be given of some image forming apparatusesincorporating the above-mentioned optical scanning apparatuses accordingto the present invention.

An image forming apparatus according to the present invention comprisesone of the above-mentioned optical scanning apparatus, a photoreceptorfor forming an electrostatic latent image, a developing apparatus fordeveloping the electrostatic latent image with a toner, a transferringapparatus for transferring the developed toner image to a recordingpaper, and a fixing apparatus for fixing the transferred toner image onthe recording paper. In this configuration, the image forming apparatuscan improve the printing speed and the printing density bysimultaneously scanning an image surface with a plurality of beams.Since the optical scanning apparatus according to the present inventionsuccessfully suppresses misalignment of optical spots on the scannedsurface 16 or a photoreceptor as mentioned above, the image formingapparatus can create a higher-quality image.

The detection timing of optical spots may be before or after an operatorpushes the start button of the image forming apparatus so as to printout the image. Also, when the image forming apparatus prints out a largenumber of sheets, the optical spot alignment may be detected for everyseveral sheets or every dozens of sheets. In addition, if an electronicsignal is not supplied to a liquid crystal element serving as a liquidcrystal deflecting element when the printing operation is not beingperformed, that is, when the beams is not scanning an image surface, theimage forming apparatus additionally may include the function for savingthe previous adjustment values.

When one of the optical scanning apparatuses according to the presentinvention is used as an optical writing apparatus of an image formingapparatus, the image forming apparatus can output an evaluation chart(output image) by operator's manipulations through an operation panel onthe body of the image forming apparatus. Here, the evaluation chart mayfollow a pattern according to Japanese Laid-Open Patent Application No.10-062705.

If an operator can confirm the quality of an image to be printed outwith reference to the above-mentioned evaluation chart, it is possibleto correct deterioration of the image to be printed due to not onlymisalignment of beam spots but also troubles of the other processes; thedeveloping process, the transferring process and the fixing process.

In addition, since the optical scanning apparatus according to thepresent invention may omit either or both of the beam spot alignmentdetecting part and the control part, it is possible to fabricate theoptical scanning at lower cost.

The optical scanning apparatus according to the present invention candetect beam spot alignment and adjust deflection of optical beams forevery one sheet of an output image, for every several sheets throughevery dozens of sheets thereof, or for every one job (batch).Accordingly, even if it takes several milliseconds through severalhundreds of milliseconds to adjust deflection of an optical beam, theadjustment time does not matter. As a result, the optical scanningapparatus does not have to possess a multi-layered liquid crystal unlikethe image forming device according to Japanese Laid-Open PatentApplication No. 2000-047214 because high response speed is not requiredfor the optical scanning apparatus according to the present invention.Also, the optical scanning apparatus does not have to possess adetecting part for detecting the rotational speed of the photoreceptorunlike the image forming device according to Japanese Laid-Open PatentApplication No. 2000-003110.

When the image forming apparatus according to the present invention isapplied to a multifunction machine serving as both a printer and acopier, it may be necessary to switch the pixel density between aprinter mode and a copier mode. For instance, when the pixel density isswitched between 600 dpi (dots per inch) under the printer mode and 400dpi under the copier mode, the multifunction machine can work under thepixel density suitable for each of the modes.

Also, there is a case where an image forming apparatus enables anoperator to switch the pixel density, for instance, between high-qualitymode (1200 dpi) and high-speed mode (600 dpi) in accordance withoperator's purposes through an operation panel on the image formingapparatus. In this case, the image forming apparatus can easily switchthe pixel density by driving/controlling a light path deflecting elementthereof.

A color image forming apparatus such as a digital color copier and acolor printer adopts a tandem form in which photoreceptors (forinstance, 5K, 5C, 5M and 5Y) corresponding to individual colors (forinstance, black: K, cyan: C, magenta: M and yellow: Y) are aligned in atandem form in the carrier direction. In this case, individual opticalscanning apparatuses (for instance, 10K, 10C, 10M and 10Y) may beprovided corresponding to the colors as shown in FIG. 33A. Also, oneoptical scanning apparatus 10A integrally corresponding to the colorsmay be provided as shown in FIG. 33B. Furthermore, two optical scanningapparatuses (a pair of 10A1 and 10A2 and a pair of 10B1 and 10B2) may beprovided as shown in FIGS. 33C and 33D. Here, although FIGS. 33A through33D illustrates only the four photoreceptor drums 5K, 5C, 5M and 5Y andthe optical scanning apparatuses, the color image forming apparatusincludes a conventional charging apparatus, a conventional developingapparatus, a conventional transferring apparatus, a conventionalcleaning apparatus and a conventional electricity removing apparatusaround each of the photoreceptor drums 5K, 5C, 5M and 5Y. Each tonerimage corresponding to the colors; black, cyan, magenta and yellow isformed on the individual photoreceptor drums; 5K, 5C, 5M and 5Y throughan electrophotographic process including a charging process, an opticalwriting process and a developing process. These toner images aresequentially superposed and transferred on an image recording mediumsuch as a recording paper that is sequentially carried among the fourphotoreceptor drums. Then, the recording paper on which the four-colortoner image has been transferred is carried to a fixing apparatus thatis not illustrated in FIGS. 33A through 33D. Finally, a color image isobtained after the fixing apparatus fixes the four-color toner image onthe recording paper.

In such a configuration, the color image forming apparatus produces acolor image at four times as speed as an 1-photoreceptor drum type colorimage forming apparatus, because the 1-photoreceptor drum type colorimage forming apparatus has to write an image in a recording paper fourtimes corresponding to the four colors.

If an image forming apparatus includes the optical scanning apparatuses10K, 10C, 10M and 10Y each of which emits just one optical beam, theimage forming apparatus can produce a full-color (four colors) image. Onthe other hand, if an image forming apparatus uses a 4-beam opticalscanning apparatus according to the present invention instead of atleast one of the optical scanning apparatuses 10K, 10C, 10M and 10Y, forinstance, the optical scanning apparatus 10K corresponding to black, itis possible to quadruple the density of the full-color image. Also, ifthe carrying speed of a recording medium is quadrupled, it is possibleto print out the fourfold number of output images. Furthermore, even ifa color image forming apparatus is used, there are many opportunitieswhere a character-based image is provided to the color image formingapparatus. In this case, it is required to increase the resolution ofthe character-based image. Accordingly, the color image formingapparatus can use not only the 4-beam optical scanning apparatus 10K butalso the other optical scanning apparatuses simultaneously to produce ahigher-quality output image even if the source image is formed of amixture of characters, photographs and geometrical images.

FIG. 34 shows the structure of an image forming apparatus according tothe present invention.

As is shown in FIG. 34, an image forming apparatus adopts two of theabove-mentioned optical scanning apparatuses 20. These two opticalscanning apparatuses are aligned in parallel with respect to the mainscanning direction. Then, the scanned surface 16 is divided into twoareas, and each of the optical scanning apparatuses scans one area ofthe scanned surface 16 as an effective writing breadth of the opticalscanning apparatus. When the two optical scanning apparatuses 20 areprovided in parallel with respect to the main scanning direction, it ispossible to make the effective writing breadth larger. Also, if theeffective writing breadth is set as the same size as the originaleffective writing breadth, it is possible to miniaturize an opticalelement and a deflector therein. As a result, since beam waist positionvariation due to mechanical tolerance and temperature fluctuationbecomes small, it is possible to reduce wave aberration. Here, althoughFIG. 34 illustrates only the scanned surface 16 and the two opticalscanning apparatuses 20, the image forming apparatus has a conventionalcharging apparatus, a conventional developing apparatus, a conventionaltransferring apparatus, a conventional cleaning apparatus and aconventional electricity removing apparatus around the scanned surface16. In the image forming apparatus, a toner image is formed on thephotoreceptor drum 16 through an electrophotographic process including acharging process, an optical writing process and a developing process.This toner image is transferred on an image recording medium such as arecording paper that is sequentially carried among the fourphotoreceptor drums. Then, the recording paper on which the toner imagehas been transferred is carried to a fixing apparatus that is notillustrated in FIG. 34. Finally, an output image is obtained after thefixing apparatus fixes the toner image on the recording paper.

A description will now be given of a correction method for correctingbeam spot alignment on a surface to be scanned by using a conventionalliquid crystal element driven by an electronic signal. In thiscorrection method, a liquid crystal element is used as a light pathdeflecting element to deflect an optical beam by a slight angle. Such aliquid crystal element is provided at or immediately behind anilluminant part so as to adjust beam spot alignment on a surface to bescanned.

In the case where a liquid crystal element is used to deflect a lightpath, it is necessary to coincide the plane of polarization of anoptical beam with an optical axis of the liquid crystal element.However, the above-mentioned correction method is limited to a situationwhere the active layer direction, that is, the polarization plane, of asemiconductor laser chip is orthogonal to the optical axis direction ofthe liquid crystal element.

FIG. 35 is a sectional view of a conventional liquid crystal elementthat is used as a light path deflecting element. As is shown in FIG. 35,the liquid crystal element is formed by sandwiching a homogeniousmolecule arrangement type nematic liquid crystal layer 201 between twoglass substrates 2U and 2D. Two transparent metal oxide electrodes 3Uand 3D are provided on the inner surfaces of the glass substrates 2U and2D, respectively.

Normally, a uniform earth electrode for forming an electronic groundsurface is provided on the whole surface of the glass substrate 2D, andon the other hand, an upper surface electrode for forming an electricfield distribution necessary for the liquid crystal layer 201 isprovided on the glass substrate 2U. In FIG. 35, the earth electrode andthe upper surface electrode are designated as the reference numerals 3Dand 3U, respectively. As is shown in FIG. 36, for instance, the uppersurface electrode 3U has a stripe electrode pattern. Here, the groundelectrode 3D and the upper surface electrode 3U are formed astransparent electrodes.

When a driving alternate voltage, for instance, a rectangular wave atseveral KHz, is applied between the ground electrode 3D and the uppersurface electrode 3U, nematic liquid crystal molecules 101 a areinclined along the electric field in the nematic liquid crystal layer101 having a birefringent index, that is, a refractive index differencebetween the major axis and the minor axis of the nematic liquid crystalmolecules 101 a. FIG. 35 schematically shows this situation. In FIG. 35,the left side shows nematic molecules 101 a in a case where the applieddriving voltage is equal to 0V. In this case, the nematic molecules 101a persist an initial orientation angle p thereof. In contrast, the rightside shows nematic molecules 101 a in a case where the applied drivingvoltage is more than Vth (the threshold value). In this case, thenematic molecules 101 a are partially inclined toward the initialorientation angle p.

In such inclined nematic molecules 101 a, the nematic liquid crystallayer 101 is equivalent to a medium having a locally differentrefractive index in accordance with the electric field for single-colorlight having straight polarization parallel with the optical axis of theliquid crystal molecules. Thus, spatial wave modulation or spatial phasemodulation is added to a wave front of light transmitting the nematicliquid crystal layer 101 in accordance with a surface distribution of anapplied voltage to the liquid crystal.

FIG. 37 shows an electronic optical characteristic of a homogeneousalignment type nematic liquid crystal. In FIG. 37, an effectivebirefringence index Dn, which is a birefringence index under whichentrance light that varies in accordance with a gradient of the majoraxis of the liquid crystal molecule is effectively influenced, isillustrated with respect to levels of the phase modulation and levels ofthe applied voltage. The shape of the electronic optical characteristicis determined based on an elastic constant, anisotropy of a dielectricconstant, and the initial orientation angle p of the liquid crystalmolecule when a voltage is not applied. Regarding the liquid crystalmolecule having the small initial orientation angle p less than 5 deg,the electronic optical characteristic drastically decreases at a point(threshold) in a low-voltage area. As the applied voltage is increased,the curve becomes approximate linear and then the electronic opticalcharacteristic is saturated toward a constant value. In contrast,regarding the liquid crystal element having the large initialorientation angle p equal to 15 deg, the electronic opticalcharacteristic does not have such a threshold. In a low-voltage area,the curve approximates to a quadratic curve.

As is shown in FIG. 36, the upper surface electrode 3U has the stripepattern in which a large number of thread-shaped electrodes are arrangedin a stripe form. Some researchers in U.S. have designed such a stripepattern electrode in which a predetermined level of voltage is appliedto each of the thread-shaped electrodes. In such an electrode, it ispossible to achieve a high-speed response, high spatial resolving powerand wide freedom of wave modulation in that a complicated wavemodulation is possible through other means other than beam deflectionand lens functions.

When a liquid crystal element is used as a light path deflecting part,the liquid crystal element adopts stripe-shaped electrode design asshown in FIG. 36 so as to make use of the linear area of the electronicoptical characteristic. The upper surface electrode 3U is formed byarranging thread-shaped electrodes having a breadth at an interval on abeam irradiation area 104 of the liquid crystal element depending on theresolving power under the current exposure technology.

In FIG. 36, the symbols A and B indicate end parts of the period D ofthe stripe upper surface electrode 3U. The end parts A and B areconnected to two inclined potential electrodes extending in thehorizontal direction outside the irradiation area 104. Accordingly, theupper surface electrode 3U has the overall structure in which severalelectrodes are aligned as a ladder. The number of bundled thread-shapedelectrodes is determined based on a maximum beam deflection angle neededin the area.

FIG. 38 shows an example of a phase distribution. When a drivingcircuit, which is not illustrated in FIG. 36, applies two distinctlevels of voltage within the linear areas of electronic opticalcharacteristics to the end parts A and B, an obtained blade-shaped phaseprofile as shown in FIG. 38 is equivalent to a microprism array. As isshown in a reference, the blade angle is changed by controlling theapplied voltage, it is possible to control the direction of an opticalbeam vertically entering the nematic liquid crystal layer 101.

In general, the main scanning direction and the subscanning directionmean the direction where a beam spot scans a surface and the directionorthogonal to the main scanning direction, respectively. However, in thefollowing, the main scanning direction and the subscanning directionmean the main scanning direction and the subscanning direction withrespect to individual spots in a light path, respectively.

FIG. 39 is a perspective view of an optical scanning apparatus accordingto the fourth embodiment. Here, the optical scanning apparatus is formedof a 2-beam scanning apparatus for scanning a surface to be scanned bysimultaneously using two optical beams. However, the optical scanningapparatus may be formed of a multi-beam scanning apparatus using morethan 2 beams.

Two semiconductor lasers 11 a and 11 b emit laser light. Two couplinglenses 112 a and 112 b couple the emitted laser light, and the coupledlaser light results in two optical beams 121 a and 121 b. The opticalbeams 121 a and 121 b are shaped into a linear form by a cylindricallens 113, and the linear optical beam is projected on a deflectingreflection surface of a polygon mirror 114, which serves as a deflector,in order to produce an optical beam that is focused on the subscanningdirection and is linearly formed with respect to the main scanningdirection. Then, the deflected linear optical beam is projected to anoptical scanning system 115 formed of a scanning lens such as an fθ lensand a toroidal lens in order to provide beam spots on a scanned surface116 f formed of the outer surface of a photoreceptor drum 16. Thisscanning direction is parallel with the axis direction of thephotoreceptor drum 116 and is called the main scanning direction.Furthermore, the direction orthogonal to the main scanning direction onthe outer surface of the photoreceptor drum 116 is called thesubscanning direction.

In this fashion, an optical scanning apparatus 120 scans the scannedsurface 116 f by using beam spots formed of the optical beams 121 a and121 b emitted from an illuminant formed of the semiconductor lasers 111a and 111 b.

Here, the optical scanning apparatus 120 is designed so that the twooptical beams 121 a and 121 b cross with each other around thedeflecting reflection surface of the polygon mirror 114 with respect toa main scanning section parallel with a virtual plane orthogonal to therotation axis Q-Q of the polygon mirror 114. In this configuration, itis possible to suppress difference of optical characteristics such as aimaging position and magnification between the two optical beams causedby difference between reflection points thereof on the polygon mirror114.

In order to correct initial arrangement of beam spot positions oroptical beam pitches on a scanned surface and misalignment caused byenvironmental fluctuation and time passage, an optical beam positioncorrecting part is often provided in an optical scanning apparatusincluding a multi-beam scanning apparatus for scanning the scannedsurface by using a large number of optical beams.

For this optical beam position adjustment, there are some conventionallight path deflecting methods for deflecting a light path of the opticalbeam by a slight angle. As the first method, the light path is deflectedby rotating a folded mirror. As the second method, the light path isdeflected by shifting or rotating a cylindrical lens. As the thirdmethod, the light path is deflected by shifting or rotating a prism. Asthe fourth method, the light path is deflected by using an electronicoptical element or AOM (Acousto-Optic light Modulator). As the fifthmethod, the light path is deflected by rotating a plane plate providedbetween a semiconductor laser and a coupling lens.

As is shown in FIG. 39, in the optical scanning apparatus according tothis embodiment, liquid crystal elements 143 a and 143 b are providedbetween the coupling lenses 112 a and 112 b and the cylindrical lens113. The liquid crystal element has some advantages. If the liquidcrystal element is used as the light path deflecting part, it ispossible to provide a small, lightweight, and energy-saving opticalscanning apparatus. In addition, the liquid crystal element generates nonoise and no heat.

Desired refractive indexes are obtained for the liquid crystal elements143 a and 143 b by properly controlling an applied driving voltage. As aresult, it is possible to adjust irradiation positions of optical beamson the scanned surface.

When the liquid crystal element is used as the light path deflectingpart, it is possible to provide an optical scanning apparatus that canenjoy the above-mentioned greater advantages than optical scanningapparatus using conventional light path deflecting parts.

As mentioned above, when a liquid crystal element is used to deflect alight path, it is necessary to coincide the optical axis of the liquidcrystal element with the polarization plane of the optical beam havinglinear polarization.

In this embodiment, a light rotating part is used to rotate thepolarization plane of the optical beam and coincide the polarizationplane of the optical beam with the optical axis of the liquid crystalelement. When the light rotating part is used to rotate the polarizationplane of the optical beam and coincide the polarization plane of theoptical beam with the optical axis of the liquid crystal element, it ispossible to efficiently deflect the light path of the optical beam andadjust controllable beam spot positions on the scanned surface.

In this embodiment, a ½ wavelength plate is used as the light rotatingpart. In detail, the liquid crystal elements 143 a and 143 b areprovided in a light path of the optical beams 121 a and 121 b betweenthe coupling lenses 112 a and 112 b and the cylindrical lens 113, and ½wavelength plates 122 a and 122 b are provided as the light rotatingpart for rotating the polarization plane of an optical beam in the upperstream side of the liquid crystal elements 143 a and 143 b.

Here, the optical beam 121 a passes through the coupling lens 112 a, the½ wavelength plate 122 a and the liquid crystal element 143 a in thesequence. On the other hand, the optical beam 121 b passes through thecoupling lens 112 b, the ½ wavelength plate 122 b and the liquid crystalelement 143 b in the sequence.

Such a ½ wavelength plate is affordable and small. As a result, when the½ wavelength plates 122 a and 122 b are used as the light rotating part,it is possible to not only easily rotate the polarization plane of anoptical beam but also fabricate a smaller optical scanning apparatus atlower cost.

The ½ wavelength plates 122 a and 122 b rotates the polarization planesof the optical beams 121 a and 121 b by a fixed angle. Now, it issupposed that the optical axis direction of the liquid crystal elementsand the oscillation direction of the optical beam emitted from theilluminant are known. Also, the fixed rotation angle of the polarizationplane is supposed to be known. Therefore, if the ½ wavelength plates aremounted at appropriate angles, it is possible to coincide thepolarization plane of the optical beam with the optical axis direction.

The installation of the ½ wavelength plates involves some mechanicalerrors. A rotation adjusting part holds the ½ wavelength plates 122 aand 122 b so as to slightly adjust the installation angles. As a result,it is possible to adjust the rotation in the optical axis direction.

In the case where the ½ wavelength plates 122 a and 122 b rotates bysetting the optical axis of the optical beam as the central axis of therotation, even if the polarization plane rotates in response to rotationadjustment of the semiconductor lasers 111 a and 111 b, it is possibleto coincide the optical axis of the liquid crystal element with thepolarization plane of the optical beam entering the liquid crystalelement by adjusting the rotation of the ½ wavelength plates 122 a and122 b.

A description will now be given, with reference to FIG. 40 and FIG. 41,of the rotation adjusting part wherein a body part of the opticalscanning apparatus 120 and a rotation holding member for holding the ½wavelength plate 122 a are designated by the reference numbers 105 and106, respectively. The rotation holding member 106 is formed as astepped cylinder and holds the ½ wavelength plate 122 a in the interiorof a cylinder part 106 a.

As is shown in FIG. 40 and FIG. 41, the cylinder part 106 a is joined atthe external diameter part with a holding hole formed in the body part105 in such a manner that the ½ wavelength plate 22 a can rotate.Furthermore, the direction of the axis line O of the cylinder part 106 ais positioned by pressing a stepped part of the cylinder part 106 a toan edge part of the holding hole by means of an appropriate elasticpart.

As is shown in FIG. 40, an arm 106 b extends from the rotation holdingmember 106 in the radius direction of the cylinder part 106 a and islocated in the interior of the concave part 105 a formed in the bodypart 105. The arm 106 b in the concave part 105 a is pressed from thelower side to the upper side by a spring 107 and an adjusting screw 107receives the pressure. As mentioned above, the rotation adjusting partaccording to this embodiment comprises the rotation holding member 106,the spring 107, the adjusting screw 108 and so on.

In this configuration, if the screw 108 is turned, it is possible torotate the rotation holding member 106 via the cylinder part 106 a. As aresult, it is possible to rotate the ½ wavelength plate 122 a by anarbitrary angle by the axis line O. ½ wavelength plate 122 b can berotated in the similar configuration to the ½ wavelength plate 122 a.

A description will now be given, with reference to FIG. 42 and FIG. 43,of a rotation mechanism of the polarization plane by using the 1/2wavelength plate.

In orthogonal coordinate systems in FIG. 42 and FIG. 43, the y axis isan arbitrary crystal axis of a ½ wavelength plate and the x axis is anorthogonal axis to the crystal axis of the ½ wavelength plate. In FIG.42, a linearly-polarized optical beam is radiated at the angle φ withrespect to the y axis in the first quadrant. Namely, an optical beamprescribed by a vector R enters the ½ wavelength plate wherein thevector R is inclined by the angle φ with respect to the polarizationplane. The vector R is decomposed to the vector RA with respect to the yaxis component and the vector RB with respect to the x axis component.

When this optical beam passes through the ½ wavelength plate, the vectorRA does not receive the influence of the ½ wavelength plate. As aresult, the vector RA is not transformed persists the length and thedirection of RA as shown in FIG. 43. On the other hand, the vector RBreceives the influence of the ½ wavelength plate and the phase delay ofλ/2 (=180°) is caused. As a result, as is shown in FIG. 43, the vectorRB rotates by 180° from the position before the passage of the opticalbeam, which is illustrated by the dotted line in FIG. 43 and istransformed into the vector −RB. Accordingly, the polarization plane ofthe composite vector R′ rotates from the position in the first quadrantbefore the transformation as shown in FIG. 42 to the position, which isrotated by the angle 2φ, in the third quadrant after the transformationas shown in FIG. 43. In this fashion, the polarization plane can beadjusted. Also, if the rotation adjusting part is used to rotate thepolarization plane of the optical beam by slightly rotating the ½wavelength plate, it is possible to coincide the optical axis of theliquid crystal element with the polarization plane of the optical beamat higher accuracy.

In a case where a single liquid crystal element is used to deflect alight path, it is difficult to separately deflect an optical beam withrespect to the main scanning direction and the subscanning directionbecause the deflection uses the polarization characteristic of theoptical beam. However, the deflection primarily intends to shiftpositions of beam spots on a scanned surface in the subscanningdirection. Thus, it is sufficient that a light path can be deflected inonly the subscanning section, that is, in a virtual section orthogonalto the optical beam. For instance, as is shown in FIG. 39, the ½wavelength plates 122 a and 122 b are positioned orthogonally to theoptical beams 121 a and 121 b, and the liquid crystal element ispositioned so that the optical beam can be shifted in the subscanningdirection on the scanned surface. In this example, since the light pathis deflected in the subscanning section only in the subscanningdirection, it is possible to virtually adjust the positions of theoptical beams only in the subscanning direction on the scanned surface.As a result, it is possible to eliminate some problems caused bymisalignment in the subscanning direction.

In the example shown in FIG. 39, a semiconductor laser array in which aplurality of illuminant points are arranged in an array form may be usedto emit optical beams instead of the semiconductor lasers 111 a and 111b. When a semiconductor laser array having n illuminant points is usedas an illuminant, it is possible to easily implement a multi-beamscanning by using n times as many optical beams as a single beamsemiconductor laser. In this case, it is possible to easily improve thespeed of image forming and the image density without increasingrotational speed of a polygon motor for rotating a polygon mirror as adeflector. In this fashion, since it is unnecessary to increase therotational speed of the polygon motor, it is possible to reduce someenvironmental load such as large electricity consumption, heatgeneration and noise.

In the case where a semiconductor laser array is used as an illuminantof an optical scanning apparatus, there is a probability that the arraypitch of the illuminant points of the semiconductor laser array does notcoincide with a desired array pitch of beam spots on a scanned surface.Even in the case, it is possible to use the semiconductor laser array toobtain the desired array pitch of beam spots on the scanned surface asmentioned later. In order to obtain the desired array pitch, thesemiconductor laser array is inclined in the optical axis direction ofan optical beam emitted from the semiconductor laser array. In otherword, the array direction of the illuminant points is inclined in thesubscanning direction.

FIG. 44 is a front view of a semiconductor laser array having an arrayof illuminant points. As is shown in FIG. 44, for instance, it issupposed that four illuminant points 10 of a semiconductor laser array 9are aligned in a line at an equal pitch. Here, the pitch betweenadjacent illuminant points is q in length. The alignment direction ofthe four illuminant points 10 is inclined by the angle φ with respect tothe subscanning direction and is mounted to the body part of the opticalscanning apparatus. In other word, the four illuminant points 10 isinclined in the optical axis direction of the optical beams emitted fromthe semiconductor laser array.

In this case, the pitch qZ between the illuminant points with respect tothe main scanning direction satisfies the following formula;qZ=q×cos(φ1).Furthermore, the pitch qY between the illuminant points with respect tothe subscanning direction satisfies the following formula;qY=q×sin(φ1).

Then, a subscanning magnification and a main scanning magnification ofthe optical scanning system with which the semiconductor laser 9 iscombined are designated by the notations mZ and mY, respectively. FIG.45 shows alignment of the beam spots radiated on the scanned surface.The pitch QZ between adjacent beam spots 10P with respect to the mainscanning direction satisfies the following formula;QZ=qz×mz=q×cos(φ1)×mz.The pitch QY between adjacent beam spots 10P with respect to thesubscanning direction satisfies the following formula;QY=qY×mY=q×sin(φ1)×mY.

In this fashion, it is possible to set the pitch QZ by using theinclination angle φ1 of the semiconductor laser array 9 in accordancewith the subscanning magnification mZ of the optical scanning system forthe semiconductor laser array 9.

According to this embodiment, it is possible to obtain a desired beampitch by inclining the semiconductor laser array regardless of themagnification of the optical scanning system.

Even if a semiconductor laser or a semiconductor laser array is inclinedin the optical axis direction as mentioned above, the polarization planeof an optical beam does not necessarily coincide with the optical axisof a liquid crystal element. However, in this case, a ½ wavelength plateand others can be used to rotate the polarization plane of the opticalbeam.

Here, a beam spot magnification RZ with respect to the subscanningdirection satisfies the following formula;RZ=(n−1)QZ=(n−1)×q×cos(φ1)×mz.A beam spot magnification RY with respect to the main scanning directionsatisfies the following formula;RY=(n−1)QY=(n−1)×q×sin(φ1)×mY.

FIG. 46 is a perspective view of an optical scanning apparatus accordingto another embodiment. FIG. 47 is a diagram illustrating the structurethe optical scanning apparatus according to the embodiment. In FIG. 46and FIG. 47, the optical scanning apparatus differs from the opticalscanning apparatus shown in FIG. 39 in the optical system in the upperstream side of the polygon mirror 114. Namely, the optical scanningapparatus shown in FIG. 46 and FIG. 47 uses PBS (Polarization BeamSlitter) of a beam synthesizing prism as a beam synthesizing part tosynthesize al least two optical beams emitted from two semiconductorlasers. The optical beams from the optical system scan a scanned surfacevia the polygon mirror 114.

In the optical scanning apparatus shown in FIG. 39, two optical beamscross with each other around a deflecting reflection surface of thepolygon mirror 114 on a main scanning section, that is, a virtual planeparallel with a plane orthogonal to the rotation axis Q-Q. In thisconfiguration, it is possible to reduce differences of some opticalcharacteristics. Furthermore, in order to maintain satisfactory opticalcharacteristics, that is, to decrease the difference between the twooptical beams, it is preferable to make the cross angle θ between thetwo optical beams smaller. However, since two pairs of the semiconductorlaser 111 a and the coupling lens 112 a and the semiconductor laser 111b and the coupling lens 112 b are aligned in parallel with respect tothe main scanning direction, it is necessary to set the angle θ as morethan a predetermined value.

Also, in the optical scanning apparatus shown in FIG. 46 and FIG. 47,the two pairs of the semiconductor lasers 111 a and 111 b and thecoupling lenses 112 a and 112 b are misaligned in the subscanningdirection unlike the optical scanning apparatus in FIG. 39.Subsequently, the ½ wavelength plates 122 a and 122 b and the liquidcrystal elements 143 a and 143 b are also misaligned in the subscanningdirection.

In this case, since the semiconductor lasers 111 a and 111 b and thecoupling lenses 112 a and 112 b do not interfere with each other, it ispossible to make the angle θ smaller substantially to 0 °

Here, it is necessary to synthesize the two optical beams misalignedwith respect to the subscanning direction. A beam synthesizing prism 117including a PBS surface 117-1 serves as a synthesizing part. FIG. 47shows the structure of the optical system in FIG. 46 with respect to asubscanning section. In FIG. 47, a P polarization component of anoptical beam is allowed to transmit the PBS surface 117-1, and an Spolarization component is reflected by an optical film on the PBSsurface 117-1.

In FIG. 47, the optical axis of the liquid crystal element 143 a directsthe Z direction, that is, the subscanning direction, and a light path isdeflected in a subscanning section. In this configuration, a position ofan optical beam can be shifted in only the subscanning direction on ascanned surface.

In a case where a polarization plane, that is, active layers of a laserchip, of the semiconductor lasers 111 a and 111 b are inclined in theoptical axis, it is possible to coincide the optical axis of the liquidcrystal element 143 with the inclined polarization plane of the opticalbeams by rotating the ½ wavelength plate 122 a and 122 b. Also, ifnecessary, the rotation adjusting part may be used.

After the optical beam 121 a from the semiconductor laser 111 atransmits the liquid crystal element 143 a, the optical beam 121 aenters the beam synthesizing prism 117. In the PBS surface 117-1 of thebeam synthesizing prism 117, the optical beam 121 a transmits the PBSsurface because the optical beam 121 a is P-polarized toward the PBSsurface 117-1. Then, the optical beam 121 a is radiated from the beamsynthesizing prism 117.

On the other hand, after the optical beam 121 b from the semiconductorlaser 111 b transmits the liquid crystal element 143 b, the polarizationplane of the optical beam 121 b is rotated by the angle 90° throughanother ½ wavelength plate 122 c that serves as the light rotating part.The optical beam 121 b is reflected on the PBS surface 117-1 of the beamsynthesizing prism 117 because the optical beam 121 b is S-polarizedtoward the PBS surface 117-1. Then, the reflected optical beam 121 b isradiated from the beam synthesizing prism 117.

A supplemental description will be given, with reference to FIG. 48, ofthe beam synthesis by rotating the above polarization plane. In theorthogonal coordinate system shown in FIG. 48, the arrow (a) indicatesoscillation of an optical beam under a case where the optical beamoscillates on a plane defined by the original point of the coordinatesystem and the intermediate direction between the Z direction and the Ydirection. The arrow (b) indicates oscillation of an optical beam undera case where the optical beam oscillates on a plane defined by theoriginal point of the coordinate system and the Z direction. The arrow(c) indicates oscillation of an optical beam under a case where theoptical beam oscillates on a plane defined by the original point of thecoordinate system and the Y direction.

Regarding the optical beam 121 a, when the optical beam 121 a emits fromthe coupling lens 112 a, the optical beam 121 a oscillates in thedirection indicated by the arrow (a) in FIG. 48. Then, when the opticalbeam 121 a emits from the ½ wavelength plate 122 a, the optical beam 121a oscillates in the oscillation direction indicated by the arrow (b) inFIG. 48. Also, when the optical beam 121 a emits from the liquid crystalelement 143 a and the beam synthesizing prism 117, the optical beam 121a persists the oscillation direction (b). Thus, only the optical beamoscillating in the direction (b) is allowed to transmit the PBS surface117-1.

On the other hand, regarding the optical beam 121 b, when the opticalbeam 121 b emits from the coupling lens 112 b, the optical beam 121 boscillates in the direction indicated by the arrow (a) in FIG. 48. Whenthe optical beam 112 b emits from the ½ wavelength plate 122 a, theoptical beam 112 b oscillates in the oscillation direction indicated bythe arrow (b) in FIG. 48. Then, when the optical beam 112 b emits fromthe ½ wavelength plate 122 c, the oscillation direction (b) rotates tothe direction indicated by the arrow (c) in FIG. 48. Since only theoptical beam oscillating in the direction (b) is allowed to transmit thePBS surface 117-1, the optical beam 112 b from the ½ wavelength plate122 c is reflected and then is synthesized with the optical beam 121 a.

FIG. 49 shows another example of the beam synthesis by the beamsynthesizing prism having the PBS surface.

FIG. 49 illustrates an illuminant and an optical system in this example.If the illuminant and the optical system are provided in the upperstream side of the deflector of the optical scanning apparatus shown inFIG. 39, an optical scanning apparatus according to this example isobtained. Also, the optical scanning apparatus according to this examplediffers from the optical scanning apparatus shown in FIG. 47 in that theformer does not have the liquid crystal element 143 b and the ½wavelength plate 122 c in the light path of the optical beam 121 b andhas a liquid crystal element 143 and the ½ wavelength plate 122 a in thelight path of the optical beam 121 a.

In this configuration, the optical beam 121 a from the semiconductorlaser 111 a oscillates in the direction (a). When the optical beam 121 atransmits the ½ wavelength plate 122 a, the optical beam 121 aoscillates in the direction (b) and then transmits the PBS surface117-1.

On the other hand, the optical beam 121 b from the semiconductor laser111 b oscillates in the direction (a). When the optical beam 121 btransmits the ½ wavelength plate 122 b, the oscillation direction (a)rotates to the direction (c) perpendicular to the sheet of FIG. 49.Here, the inclination of the ½ wavelength plate 122 b is set so that theoscillation direction can be properly rotated.

Since only the optical beam oscillating in the direction (b) is allowedto transmit the PBS surface 117-1, the optical beam 112 b from the ½wavelength plate 122 b is reflected and then is synthesized with theoptical beam 112 a. In this example, a beam position of the optical beam121 b is adjusted relatively to the optical beam 121 a. The beamposition is adjusted by changing the refractive index of the liquidcrystal element 143 through control of the driving voltage thereto.

FIG. 50 shows the structure of an illuminant and an optical system of a4-beam scanning apparatus to which the above-mentioned illuminants andthe optical systems provided in FIG. 47 and FIG. 49, that is, theilluminants and the optical systems for synthesizing optical beams byusing ½ wavelength plates and PBS surfaces, are applied. The 4-beamscanning apparatus is formed by mounting the illuminant and the opticalsystem shown in FIG. 50 to the upper stream side of the deflector of theoptical scanning apparatus shown in FIG. 39. In FIG. 50, optical beams121A through 121D from semiconductor lasers 111A through 111D arecoupled by coupling lenses 112A through 112D, respectively. Then,individually positioned ½ wavelength plates 122-1A through 122-1D servesas a first light rotating part to rotate light paths of the opticalbeams 121A through 121D so that the light paths can coincide with theoptical axis of the liquid crystal element 143.

Among the four optical beams 121A through 121D whose light paths havebeen deflected according to necessity, the polarization planes of theoptical beams 121C and 121D are rotated by the angle 90° by a ½wavelength plate 122-2 as a second light rotating part.

Accordingly, the polarization planes of the optical beams 121A and 121Bare orthogonal to those of the optical beams 121C and 121D. If the PBSsurface 117-1 corresponding to each pair of the polarization planes isprovided to the beam synthesizing prism 117, the beam synthesizing prismsynthesizes the optical beam 121A with the optical beam 121B and theoptical beam 121C with the optical beam 121D, respectively. Here, theoptical beams 121A and 121B correspond to the optical beam 121 a in FIG.47 because the optical beams 121A and 121B can transmit the beamsynthesizing prism 117. On the other hand, the optical beams 121C and121D correspond to the optical beam 121 b in FIG. 47 because the opticalbeams 121C and 121D are reflected on the PBS surface 117-1.

As mentioned above, if the liquid crystal element 143 is provided sothat optical beams from the liquid crystal element 143 can beS-polarized or P-polarized toward the PBS surface of a beam synthesizingprism, that is, the optical beams from the liquid crystal element 143can be reflected or transmitted toward the PBS surface, it is possibleto deflect light paths of the optical beams and synthesize the opticalbeams without the installation of an additional light rotating part suchas ½ wavelength plates between the liquid crystal element 143 and thebeam synthesizing part. Furthermore, since the beam synthesizing partuses polarization to synthesize the optical beams, it is possible toreduce energy loss in the beam synthesizing part.

FIG. 51 shows the structure of an illuminant and an optical system ofanother optical scanning apparatus in which a half-mirror 117-2 is usedas the beam synthesizing prism 117 instead of a PBS surface. The opticalscanning apparatus is formed by mounting the illuminant and the opticalsystem shown in FIG. 51 to the upper stream of the deflector of theoptical scanning apparatus shown in FIG. 39.

In FIG. 51, an optical beam 121 a from a semiconductor laser 111 a iscoupled by a coupling lens 112 a. After that, the polarization plane ofthe optical beam 121 a is rotated to the direction (b) by a ½ wavelengthplate 122 a so that the optical axis of the liquid crystal element cancoincide with the polarization plane. Then, the optical beam 121 atransmits the half-mirror 117-2 of the beam synthesizing prism 117 andtravels to the scanned surface.

An optical beam 121 b from a semiconductor laser 111 b is coupled by acoupling lens 112 b. After that, the polarization plane of the opticalbeam 121 b is rotated to the direction (b) by a ½ wavelength plate 122 aso that the optical axis of the liquid crystal element 143 can coincidewith the polarization plane. Then, the optical beam 121 b transmits thehalf-mirror 117-2 of the beam synthesizing prism 117 and travels to thescanned surface.

In this fashion, when a beam synthesizing prism uses a half-mirror tosynthesize optical beams, it is possible to synthesize the optical beamswithout dependency on the directions of the polarization planes of theoptical beams unlike the PBS surface. As a result, since it isunnecessary to provide a light rotating part such as a ½ wavelengthplate between the liquid crystal element 143 and the beam synthesizingprism 117, it is possible to reduce the fabrication cost due to thesmaller number of parts.

A description will now be given of an image forming apparatus to whichthe above-mentioned optical scanning apparatuses are applied. In thefollowing, such an image forming apparatus has a photoreceptor formingan electrostatic latent image, a developing part developing theelectrostatic latent image with a toner, and a transferring parttransferring the developed toner image on a recording paper.

In FIG. 52, process members such as a charging part, a developing part,a transferring part, a cleaning part for cleaning remaining toner andothers are provided around the photoreceptor in accordance with anelectrophotographic process. In addition, a sheet feeding part foraccommodating and supplying recording sheets such as a paper feedcassette is provided beneath a transferring belt 205. The transferringpart is provided at the position opposite to the photoreceptor in theinterior of the transferring belt 205. A belt charging part is providedin the upper side of the transferring belt 205 with respect to therotational direction indicated by the arrow in FIG. 52. A belt separatecharger, a fixing part and the like are provided in the lower side ofthe transferring belt 205. These parts are formed of conventional partsand are not illustrated in FIG. 52 for simplicity.

In the image forming apparatus according to this embodiment, the opticalscanning apparatus thereof exposes a plurality of photoreceptors inorder to form an electrostatic latent image. Then, individual visibleimages on the photoreceptors are transferred and superposed on thetransferring belt 205. After that, all the superposed images on thetransferring belt 205 are transferred on one recording sheet so as toobtain a color image.

In order to form a color difference detecting toner image, an opticalbeam is radiated for every predetermined sheets. When color differencedetecting toner images 330Z are provided at three portions of thetransferring belt 205 as shown in FIG. 52, color difference detectingsensors 330 detect a color difference of a toner image.

The optical scanning apparatus, which is formed as a unit, is located inthe upper area of photoreceptors 160Y, 160M, 160C and 160K. As is shownin FIG. 52, an illuminant and an optical system of the optical scanningapparatus are formed by double-layering the structure comprisingsemiconductor lasers 111 a and 111 b, coupling lenses 112 a and 112 b, ½wavelength plates 122 a and 122 b, and liquid crystal elements 143 a and143 b of the illuminant and the optical system as shown in FIG. 39. Inthis double layered configuration, the optical scanning apparatus usesfour optical beams to scan the surface to be scanned.

These four optical beams scan the four photoreceptors 160Y, 160M, 160Cand 160K that are aligned in a line and are rotationally driven. When animage is formed, the latent image is formed by the four optical beams asdistinct color toner images by using the four color photoreceptors 160Y,160M, 160C and 160K. After the latent image is developed, these colortoner images are superposed and transferred on the transferring belt 205as an intermediate transferred image.

Optical beams from the optical scanning apparatus travel toward thepolygon mirror 114. The optical beams are deflected by the polygonmirror 114 and then scan the photoreceptors 160Y, 160M, 160C and 160Kvia the fθ lens 120, a folded mirror 110M, troidal lens 100.

The longitudinal directions of the photoreceptors 160Y, 160M, 160C and160K correspond to the main scanning direction, and beam spot positiondetecting parts 300 a and 300 b are faced on each other corresponding toboth outer sides of effective image areas of the individualphotoreceptors. The beam spot position detecting part 300 a serves todetect a write starting position, and the beam spot position detectingpart 300 b serves to detect a write end position.

The image forming apparatus has a charging part uniformly charging thephotoreceptors 160Y, 160M, 160C and 160K before optical beams scan thephotoreceptors, a developing part developing electrostatic latent imagesformed on the photoreceptors with toners through the scanning by theoptical beams, a transferring part transferring the developed tonerimages on a recording paper, and a fixing part fixing unfixed tonerimages on the recording paper, around the photoreceptors. In the imageforming apparatus, it is possible to use a beam spot position adjustingfunction such as a liquid crystal element and a light rotating part ofthe optical scanning apparatus to adjust beam spot positions on thephotoreceptors according to necessity. As a result, it is possible tooutput a high-quality image. Furthermore, since the optical scanningapparatus according to this embodiment is formed of a multi-beamscanning apparatus capable of simultaneously scanning the photoreceptorsby using a plurality of optical beams, it is possible to enhance theprinting speed and the image density.

When the above-mentioned image forming apparatus is used in practice asa printer, a digital copier or the like, there is a probability that thebeam spot pitch adjusted before shipment is disturbed due to vibrationcaused when the image forming apparatus is carried out of a factory andconstraints on the installation location. Also, in a customer side,there is a probability that the scanning pitch is disturbed over timedue to high temperature therein caused by installation environments andby usage conditions such as pressrun.

In this case, if a detection system for detecting the scanning pitch isprovided in the image forming apparatus, it is possible to detect thedisorder of the scanning pitch resulting from the above-mentioned causesand correct the inappropriate scanning pitch by driving the liquidcrystal element based on detection results. Thus, it is possible toprovide the image forming apparatus that can produce a high-qualityimage by correcting the inappropriate scanning pitch caused by timepassage and temperature fluctuation.

When the above-mentioned image forming apparatus is used as amultifunction machine serving as both a printer and a copier, it may benecessary to switch the pixel density between a printer mode and a copymode. For instance, if the pixel density is switched between 600 dpi inthe printer mode and 400 dpi in the copier mode, it is possible to offerthe pixel density suitable to each mode.

Also, the image forming apparatus may be required to enable an operatorto switch the pixel density to levels suitable to operator's purposes,for instance, between high-quality mode (1200 dpi) and high-speed mode(600 dpi) by providing pixel density switch instruction from anoperation panel of the image forming apparatus. In this case, it ispossible to easily switch the pixel density by controlling the drivingvoltage to the liquid crystal element in the optical scanning apparatusof the image forming apparatus. For instance, in the above-mentionedmultifunction machine, when an operator switches between the printermode and the copier mode, it is possible to switch the pixel density. Insuch an image forming apparatus having two image forming functions whosepixel densities are different from each other, when an operator switchesbetween the two image forming functions, it is possible to switch thepixel density.

The above-mentioned image forming apparatus intends to produce ahigh-quality image by adjusting the beam pitch of a plurality of opticalbeams for scanning a photoreceptor drum. In addition, the image formingapparatus shown in FIG. 52 can correct the scanning line position of aplurality of photoreceptors, that is, a color difference among aplurality of image stations.

In a conventional image forming apparatus, the movement of thetransferring belt 205 is not synchronized with the phase of the rotationof the polygon mirror 114. Accordingly, there is a probability that theimage write start position with respect to the subscanning direction isdelayed by at most one scanning line among the image stations.

In the image forming apparatus shown in FIG. 52, the liquid crystalelements 143 a and 143 b are provided in light paths of optical beamstraveling to the photoreceptor drums 160K, 160C, 160M, 160Y. Each of theliquid crystal elements 143 a and 143 b may have a plurality ofeffective areas therein or may have one effective area for each laserbeam.

In this configuration, when the liquid crystal elements 143 a and 143 badjust beam spot positions on the photoreceptor drums, it is possible tocorrect differences of write start positions among image stations, thatis, relative beam spot positions among the photoreceptors, caused by theasynchronism between the movement of the transferring belt 205 and thephase of the rotation of the polygon mirror 114.

For instance, if the color difference detecting sensor 330 on thetransferring belt 205 detects a color difference detection toner image330Z for detecting color differences among the image stations and theliquid crystal elements 143 a and 143 b are driven in accordance withdetection results related to the degree of color differences among theimage stations, it is possible to correct the write start timing, thatis, the write start position, with respect to the subscanning direction.

Here, it is unnecessary to provide the liquid crystal element in alllight paths of the optical beams. A color, for instance, black, isdetermined as the reference color, and the other colors, in this case,cyan, magenta and yellow, are positioned relatively to the referencecolor. Therefore, it is sufficient to provide liquid crystal elements inonly light paths of the other colors.

In this fashion, it is possible to suppress color differences of thecolor difference detection toner image 330Z on the transferring belt 205and obtain a high-quality color image. As mentioned above, the tandemtype color image forming apparatus according to this embodiment canproduce a high-quality color image by coinciding among the write startpositions of the image stations with respect to the paper feedingdirection.

A description will be given of another example of the above-mentionedimage forming apparatus shown in FIG. 52. In this example, thephotoreceptors 160Y, 160M, 160C and 160K and the transferring belt 205are twice as long as those in FIG. 52 with respect to the main scanningdirection, and the optical scanning apparatus, the optical system andthe polygon mirror are additionally provided in the main scanningdirection.

FIG. 53 shows the structure of the image forming apparatus according tothis example. Two optical scanning apparatuses 120 and 120′ havingidentical structures are aligned toward one of the photoreceptors, forinstance, the photoreceptor 160, in a line with respect to the mainscanning direction. In this configuration, it is possible to correctmisalignment around a connecting area of the two beam spot positions.

The optical scanning apparatus 120 has semiconductor lasers 111 a and111 b, coupling lenses 112 a and 112 b, folded mirrors M1 and M2, apolygon mirror 114, a troidal lens 120 and others. Here, when theseoptical systems are used, it is possible to scan the photoreceptor 160with a plurality of optical beams. Here, although the optical scanningapparatus 120 also has a liquid crystal element, a light rotating partand the like, these parts are omitted in FIG. 52 for simplicity. Theother optical scanning apparatus 120′ has the same structure as theoptical scanning apparatus 120.

The optical scanning apparatuses 120 and 120′ aligned in a line withrespect to the main scanning direction scan a divided effective writebreadth. If a liquid crystal element is used to adjust beam spotpositions with respect to the subscanning direction, it is possible tocorrect the misalignment around the connection area 118 in FIG. 52. Itis noted that the correction of the beam spot misalignment is related toonly the subscanning direction, that is, the scanning line position.According to a division scanning type image forming apparatus using theabove-mentioned optical scanning apparatuses, it is possible to coincideamong beam spot positions around the connection areas between every twoimage stations and produce a high-quality image.

In this fashion, when several optical scanning systems are aligned inline, it is possible to extend the effective write breadth. Also, if theeffective write breadth is unchanged, it is possible to miniaturize anoptical element and a deflector in the optical scanning apparatus.Furthermore, it is possible to decrease an amount of misalignment ofbeam positions caused by mechanical tolerance and temperaturefluctuation and reduce wave front aberration. As a result, the imageforming apparatus can produce a high-quality image.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority applications No.2002-072656 filed Mar. 15, 2002, No. 2002-256704 filed Sep. 2, 2002 andNo. 2002-348581 filed Nov. 29, 2002, the entire contents of which arehereby incorporated by reference.

1. An optical scanning apparatus for scanning a surface to be scanned ina main scanning direction by simultaneously using a plurality of opticalspots formed of a plurality of optical beams emitted from an illuminantvia a polygon mirror, comprising: a light path deflecting partdeflecting a light path of at least one of said optical beams, whereinsaid light path deflecting part is provided in light paths of saidoptical beams between the illuminant and the polygon mirror, whereinsaid light path deflecting part includes a plurality of liquid crystaldeflecting elements formed of a liquid crystal element being separatelycontrollable by an electronic signal to deflect the light path of saidoptical beams.
 2. The optical scanning apparatus as claimed in claim 1,wherein said liquid crystal deflecting element is capable of deflectingoptical beams separately in two directions orthogonal to each other. 3.The optical scanning apparatus as claimed in claim 1, wherein saidliquid crystal deflecting element has a plurality of effective areaseach of which is separately modulated.
 4. The optical scanning apparatusas claimed in claim 3, wherein said liquid crystal deflecting elementhas a plurality of effective areas where said liquid crystal deflectingelements are capable of deflecting different optical beams separately,and the plurality of effective areas are two-dimensionally arranged. 5.The optical scanning apparatus as claimed in claim 1, wherein saidilluminant comprises at least a semiconductor laser serving as anilluminant point and a coupling lens coupling laser light emitted fromsaid semiconductor laser.
 6. The optical scanning apparatus as claimedin claim 1, further comprising a beam synthesizing part synthesizingoptical beams emitted from a plurality of illuminants.
 7. The opticalscanning apparatus as claimed in claim 6, wherein each of saidilluminants comprises at least a semiconductor laser serving as anilluminant point and a coupling lens coupling laser light emitted fromsaid semiconductor laser, and said semiconductor and said coupling lensare arranged so as to correct a synthesis error by said beamsynthesizing part.
 8. The optical scanning apparatus as claimed in claim1, further comprising an aperture member having an aperture for shapingan optical beam wherein said aperture member is provided in an upperstream side, that is, in an illuminant side, of the liquid crystaldeflecting element in the light paths of the optical beams.
 9. Theoptical scanning apparatus as claimed in claim 8, wherein said aperturefor shaping an optical beam is formed on one of an entrance surface andan exit surface of said liquid crystal deflecting element.
 10. Theoptical scanning apparatus as claimed in claim 1, further comprising adetecting part detecting positions of said optical spots forsimultaneously scanning said surface to be scanned and a driving partdriving/controlling a liquid crystal deflecting element based on adetection result of said detecting part so as to adjust a position of atleast one of said optical spots.
 11. An illuminant apparatus foremitting a plurality of optical beams and serving an optical scanningapparatus for scanning a surface to be scanned in a main scanningdirection by simultaneously using a plurality of optical spots formed ofsaid optical beams emitted from a plurality of illuminants therein,wherein said optical scanning apparatus comprises a light pathdeflecting part, which is provided in light paths of said optical beams,deflecting a light path of at least one of said optical beams, saidlight path deflecting part configured to adjust a deflecting directionof the optical beams, comprising: a plurality of light path deflectingparts separately provided for deflecting one of said optical beamscorresponding to each of said light path deflecting parts to enable alight path emitted from one illuminant to be deflected separately fromthe other illuminants, wherein said light path deflecting parts areintegrally provided.
 12. The illuminant apparatus as claimed in claim11, wherein said light path deflecting part is formed of a transmissiontype optical element and is provided in light paths of the opticalbeams.
 13. The illuminant apparatus as claimed in claim 11, wherein saidlight path deflecting part is formed of a reflection type opticalelement and is provided in light paths of the optical beams.
 14. Theilluminant apparatus as claimed in claim 12, wherein said transmissiontype optical element is driven by a driving part using a piezoelectricelement.
 15. The illuminant apparatus as claimed in claim 13, whereinsaid reflection type optical element is driven by a driving part using apiezoelectric element.
 16. The illuminant apparatus as claimed in claim12, wherein said transmission type optical element is driven by adriving part using one of a pulse motor capable of rotating by apredetermined angle in accordance with an input pulse signal and a pulsemotor capable of moving straight by a predetermined distance inaccordance with an input pulse signal.
 17. The illuminant apparatus asclaimed in claim 13, wherein said reflection type optical element isdriven by a driving part using one of a pulse motor capable of rotatingby a predetermined angle in accordance with an input pulse signal and apulse motor capable of moving straight by a predetermined distance inaccordance with an input pulse signal.
 18. The illuminant apparatus asclaimed in claim 11, wherein said light path defecting part is formed ofa liquid crystal element driven by an electronic signal.
 19. Theilluminant apparatus as claimed in claim 11, further comprising a firstilluminant part integrally having a plurality of illuminants aligned inline in the main scanning direction, a second illuminant part integrallyhaving a plurality of illuminants aligned in line in the main scanningdirection, and a beam synthesizing part making optical beams emittedfrom said first illuminant part and said second illuminant part close toeach other and emitting said close optical beams.
 20. The illuminantapparatus as claimed in claim 11, wherein said illuminants comprises aplurality of semiconductor lasers and a plurality of coupling lensescorresponding to said semiconductor lasers.
 21. The illuminant apparatusas claimed in claim 11, further comprising an aperture member having anaperture for shaping an optical beam, wherein said aperture member isprovided in an upper steam side, that is, an illuminant side, of saidlight path deflecting parts.
 22. An optical scanning apparatus forscanning a surface to be scanned in a main scanning direction bysimultaneously using a plurality of optical spots formed of a pluralityof optical beams emitted from a plurality of illuminants in anilluminant apparatus wherein said illuminant apparatus comprises aplurality of light path deflecting parts, which is integrally providedtherein, separately provided for deflecting one of said optical beamscorresponding to each of said light path deflecting parts to enable alight path emitted from one illuminant to be deflected separately fromthe other illuminants, comprising: a detecting part detecting positionsof said optical spots for simultaneously scanning said surface to bescanned; and a driving part driving/controlling said light pathdeflecting parts based on a detection result of said detecting part soas to adjust a position of at least one of said optical spots; adeflector deflecting said optical beams emitted from said illuminants;and a scanning type imaging system scanning said surface to be scannedby using said optical spots formed of said optical beams deflected,wherein said optical beams from said illuminants enter said deflectornon-parallel with each other with respect to the main scanning section.23. The optical scanning apparatus as claimed in claim 22, furthercomprising a deflector deflecting said optical beams emitted from saidilluminants and a scanning type imaging system scanning said surface tobe scanned by using said optical spots formed of said optical beamsdeflected, wherein said optical beams from said illuminants enter saiddeflector non-parallel with each other with respect to the main scanningsection.
 24. The optical scanning apparatus as claimed in claim 1,further comprising an illuminant apparatus formed of a plurality ofilluminants, a beam synthesizing part synthesizing a plurality ofoptical beams emitted from said illuminant apparatus, a deflectordeflecting said optical beams synthesized by said beam synthesizingpart, and a scanning part leading said optical beams deflected by saiddeflector on said surface to be scanned, wherein said light pathdeflecting part is provided between said illuminants and said beamsynthesizing part so as to adjust positions of said optical beams onsaid surface to be scanned.
 25. The optical scanning apparatus asclaimed in claim 24, wherein said light path deflecting part is formedof a transmission type optical element that is eccentrically provided.26. The optical scanning apparatus as claimed in claim 24, wherein saidlight path deflecting part is formed of a liquid crystal elementcontrollable by an electronic signal.
 27. The optical scanning apparatusas claimed in claim 26, further comprising a ghost light removing partremoving ghost light caused by said liquid crystal element, wherein saidghost light removing part is provided as a slit aperture between saidliquid crystal element and said deflector.
 28. The optical scanningapparatus as claimed in claim 27, further comprising an aperture shapingan optical beam, wherein said aperture is provided in an upper streamside, that is, an illuminant side, of said light path deflecting partand the following formula is satisfied;L≧(b+Δ)/(2×tan θ), where b is a width of optical beams deflected by saidliquid crystal element, Δ is a width of said slit aperture, L is adistance between said liquid crystal element and said slit aperture, and2 θ is an angle between +1st-order light and -1st-order light of saidghost light caused by said liquid crystal element.
 29. The opticalscanning apparatus as claimed in claim 24, further comprising an opticalhousing accommodating parts thereof, wherein said optical housing holdssaid illuminant apparatus on a side wall thereof and holds said lightpath deflecting part and said beam synthesizing part on a common holdingpart therein.
 30. An image forming apparatus for forming an image,comprising: an optical scanning apparatus for scanning a surface to bescanned in a main scanning direction by simultaneously using a pluralityof optical spots formed of a plurality of optical beams emitted from anilluminant including a plurality of light path deflecting partsdeflecting a light path of at least one of said optical beams, whereinsaid light path deflecting parts are provided in light paths of saidoptical beams and enable a light path emitted from one illuminant to bedeflected separately from the other illuminants; a photoreceptor formingan electrostatic latent image scanned by said optical scanningapparatus; a developing apparatus developing said electrostatic latentimage as a toner image with a toner; and a transferring apparatustransferring said toner image in a recording medium.
 31. An imageforming apparatus for forming an image, comprising: an optical scanningapparatus for scanning a surface to be scanned in a main scanningdirection by simultaneously using a plurality of optical spots formed ofa plurality of optical beams emitted from a plurality of illuminants inan illuminant apparatus wherein said illuminant apparatus comprises aplurality of light path deflecting parts, which are integrally providedtherein, deflecting one of said optical beams corresponding to each ofsaid light path deflecting parts separately to enable a light pathemitted from one illuminant to be deflected separately from the otherilluminants, comprising a detecting part detecting positions forsimultaneously scanning said surface to be scanned and a driving partdriving/controlling said light path deflecting parts based on adetection result of said detecting part so as to adjust a position of atleast one of said optical spots; a photoreceptor forming anelectrostatic latent image scanned by said optical scanning apparatus; adeveloping apparatus developing said electrostatic latent image as atoner image with a toner; and a transferring apparatus transferring saidtoner image in a recording medium.
 32. The image forming apparatus asclaimed in claim 30, wherein said light path deflecting part isdriven/controlled by an operator based on an output image on saidrecording medium.
 33. The image forming apparatus as claimed in claim30, further comprising a plurality of said photoreceptors serving as aplurality of surfaces to be scanned.
 34. The image forming apparatus asclaimed in claim 30, further comprising a plurality of said opticalscanning apparatuses wherein said optical scanning apparatuses arealigned in line in the main scanning direction for said photoreceptor.35. The image forming apparatus as claimed in claim 30, wherein saidimage has variable pixel density.
 36. An optical scanning apparatus asclaimed in claim 1, further comprising: a light rotating part rotating apolarization plane of said optical beam in such a way that thepolarization plane of said optical beam is parallel with an optical axisof the liquid crystal element.
 37. The optical scanning apparatus asclaimed in claim 36, wherein said light rotating part is formed of a ½wavelength plate.
 38. The optical scanning apparatus as claimed in claim37, wherein said ½ wavelength plate is held by a rotation adjusting partand is capable of rotating upon an optical axis.
 39. The opticalscanning apparatus as claimed in claim 36, wherein a position of saidoptical spot is adjusted on the surface to be scanned by deflecting alight path of said optical beam in a subscanning section of said liquidcrystal element.
 40. The optical scanning apparatus as claimed in claim36, wherein said semiconductor laser is formed of a semiconductor laserarray having a plurality of illuminant points.
 41. The optical scanningapparatus as claimed in claim 40, wherein said semiconductor laser arrayis inclined toward an optical axis of said optical beam emitted.
 42. Theoptical scanning apparatus as claimed in claim 39, wherein said surfaceto be scanned is scanned by an optical beam synthesized from at leasttwo optical beams emitted from at least two semiconductor lasers byusing a PBS (Polarization Beam Splitter) surface, and said liquidcrystal element is arranged so as to convert an optical beam emittedfrom said liquid crystal element into one of an S-polarized optical beamor a P-polarized optical beam toward said PBS surface.
 43. The opticalscanning apparatus as claimed in claim 39, wherein said surface to bescanned is scanned by an optical beam synthesized from at least twooptical beams from at least two semiconductor lasers by using ahalf-mirror.
 44. An image forming apparatus for forming an image,comprising: an optical scanning apparatus for scanning a surface to bescanned by using an optical spot formed of an optical beam emitted froma semiconductor laser, the optical scanning apparatus comprising a lightpath deflecting part including a plurality of liquid crystal elementsdeflecting a light path of said optical beam on said surface to bescanned and a light rotating part rotating a polarization plane of saidoptical beam in such a way that the polarization plane of said opticalbeam is in parallel with an optical axis of the liquid crystal element;a photoreceptor forming an electrostatic latent image scanned by saidoptical scanning apparatus; a developing part developing saidelectrostatic latent image as a toner image with a toner; and atransferring part transferring said toner image in a recording medium.45. The image forming apparatus as claimed in claim 44, wherein saidoptical scanning apparatus scans said photoreceptor by using a pluralityof beam spots formed of a plurality of optical beams and is capable ofadjusting a scanning line pitch on said photoreceptor.
 46. The imageforming apparatus as claimed in claim 44, wherein said optical scanningapparatus scans said photoreceptor by using a plurality of optical beamsand is capable of switching a pixel density of the image.
 47. A tandemtype image forming apparatus for forming an image, comprising: anoptical scanning apparatus for scanning a surface to be scanned by usinga beam spot formed of an optical beam emitted from a semiconductorlaser, the optical scanning apparatus comprising a plurality of liquidcrystal deflecting elements deflecting a light path of said optical beamon said surface to be scanned; and a light rotating part rotating apolarization plane of said optical beam in such a way that thepolarization plane of said optical beam is in parallel with an opticalaxis of the liquid crystal element; a photoreceptor forming anelectrostatic latent image scanned by said optical scanning apparatus; adeveloping part developing said electrostatic latent image as a tonerimage with a toner; and a transferring part transferring said tonerimage in a recording medium, wherein a plurality of said photoreceptorsare provided, said optical scanning apparatus scans said photoreceptorswith a plurality of optical beams, and misalignment of a write startposition between said photoreceptors is corrected.
 48. A divisionscanning type image forming apparatus for forming an image, comprising:an optical scanning apparatus for scanning a surface to be scanned byusing a beam spot formed of an optical beam emitted from a semiconductorlaser, the optical scanning apparatus comprising a plurality of liquidcrystal deflecting elements deflecting a light path of said optical beamon said surface to be scanned and a light rotating part rotating apolarization plane of said optical beam; a photoreceptor forming anelectrostatic latent image scanned by said optical scanning apparatus; adeveloping part developing said electrostatic latent image as a tonerimage with a toner; and a transferring part transferring said tonerimage in a recording medium, wherein a plurality of said opticalscanning apparatuses are aligned in line with respect to a main scanningdirection for each photoreceptor and misalignment of said beam spot withrespect to a main scanning direction around a connection area betweenscanning beams from said optical scanning apparatuses is corrected. 49.The division scanning type image forming apparatus as claimed in claim48, wherein said misalignment of the beam spot around a connection areabetween scanning beams is corrected with respect to a subscanningdirection.
 50. The illuminant apparatus as claimed in claim 12, whereinthe transmission type optical element is driven by a ring ultrasoundmotor.
 51. The illuminant apparatus as claimed in claim 13, wherein thereflection type optical element is driven by a ring ultrasound motor.52. The illuminant apparatus as claimed in claim 18, wherein the liquidcrystal element has a plurality of effective areas where differentoptical beams are enabled to be individually deflected, and theplurality of effective areas are two dimensionally arranged.